WHY THE FEDERAL RESERVE
SHOULD ADOPT INFLATION TARGETING
Frederic S. Mishkin
Uris Hall 619
Columbia University
New York, New York 10027
Phone: 212-854-3488, Fax: 212-316-9219
E-mail: fsm3@https://www.doczj.com/doc/aa18634067.html,
January 2004
Any views expressed in this paper are those of the author only and not those of Columbia University or the National Bureau of Economic Research.
Under Alan Greenspan, the Federal Reserve has achieved extraordinary economic performance: inflation has become low and stable, while over the last twenty years the economy has experienced only two relatively mild recessions in 1990-91 and 2001. Although the Federal Reserve has not articulated an explicit strategy, a coherent strategy for the conduct of monetary policy exists nonetheless. This strategy involves an implicit, but not an explicit nominal anchor in the form of an overriding concern by the Federal Reserve to control inflation in the long run. In addition it involves forward-looking behavior in which there is careful monitoring for signs of future inflation using a wide range of information, coupled with periodic "pre-emptive strikes" by monetary policy against the threat of inflation or deflation.
Because of the long lags from monetary policy to aggregate economic activity and inflation, monetary policy needs to be forward-looking and preemptive: that is, depending on the lags from monetary policy to inflation, monetary policy needs to act well before inflationary or deflationary pressures appear in the economy. For example, suppose it takes roughly two years for monetary policy to have a significant impact on inflation. In this case, even if inflation is currently low but policymakers believe inflation will rise over the next two years, they must now tighten monetary policy to prevent the inflationary surge. This is exactly what the Fed has done. For example, the Fed raised the federal funds rate from 3 to 6% from February 1994 to February 1995 before a rise in inflation got a toehold. As a result, inflation not only did not rise, but fell slightly. In January 2001, the Fed reversed course extremely rapidly, cutting the federal funds rate by 100 basis points (1 percentage point) in January even before the business cycle peak in March, and then proceeded to cut the fed funds rate by another 350 basis points before the end of November when the NBER declared that a recession had indeed occurred. The recession then turned out to be very mild, especially given the adverse shocks of the September 11 terrorist attacks and the negative impacts of the Enron and other corporate scandals on the credit markets.
The main argument for the the Fed’s pre-emptive monetay policy strategy, which I like
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to call the "just do it" approach, is simply its demonstrated success. In addition, the approach is flexible and appropriately makes use of all available information in setting policy instruments.
A natural question to ask then is why the Federal Reserve should consider any other other monetary policy strategy. In other words, "If it ain't broke, why fix it?" The answer is that the "just do it" strategy has some disadvantages that may cause it to work less well in the future, particularly when Alan Greenspan steps down from the Fed, something that will almost surely occur by the time his term expires in two years.
An important disadvantage of the "just do it" strategy is a lack of transparency. The constant guessing game about the Fed's goals created by its close-mouthed approach creates unnecessary volatility in financial markets and arouses uncertainty among producers and the general public. A case in point is the recent sharp swings in long-term interest rates during the late spring and summer of 2003: because the market was confused about the Fed’s intentions, the ten-year bond rate dropped from a level near 4% at the beginning of May to 3.2% in the middle of June and then rose over 100 basis points to 4.5% by the end of July. The Fed has been struggling recently with how to communicate its plans with regard to interest-rate policy and how it should structure its formal statement immediately after each FOMC meeting. If the markets had a clearer picture of the Fed’s longer-run objectives, particularly on inflation, then they would focus less on what the Fed’s next policy move would be, making it less likely that Fed policy moves or changes in its formal statement would lead to whipsawing of the market.
In addition, the opacity of its policymaking is hardly conducive to making the Federal Reserve accountable to Congress and the general public: The Fed can’t be held accountable if there are no predetermined criteria for judging its performance. This lack of accountability also is inconsistent with democratic principles. There are good reasons – notably, insulation from short-term political pressures – for the central bank to have a high degree of independence, as the Federal Reserve currently does, and empirical evidence does generally support central bank
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1For example, see Alesina and Summers (1993), Cukierman (1992), and Fischer (1994).However, there is some question whether causality runs from central bank independence to low inflation, or rather, whether a third factor is involved, such as the general public's preferences for low inflation that create both central bank independence and low inflation (Posen, 1995). 2Woodward (2000).
3See Goodfriend (forthcoming).
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independence.1 Yet the practical economic arguments for central bank independence coexist uneasily with the presumption that government policies should be made democratically, rather than by an elite group.
The lack of an explicit nominal anchor is also a potential problem for the "just do it"strategy: For example, it may be that the Fed risks greater exposure than is necessary to "inflation scares" -- the spontaneous increases in inflation fears described by Goodfriend (1993)that can become self-justifying if accommodated by the Fed. Indeed, as Goodfriend (forthcoming) points out, even Alan Greenspan faced an inflation scare shortly after becoming the Fed Chairman.
Probably the most serious problem with the "just do it" approach is that its success is based on highly capable individuals rather than good institutions. In the United Sates, Federal Reserve Chairman Alan Greenspan and other Federal Reserve officials have emphasized forward-looking policies and inflation control, which has been key elements in their success.The Fed's prestige and credibility with the public have risen accordingly, with Greenspan having been given the title of “maestro” in the media.2 I have acknowledged elsewhere in Mishkin (2000) that the Fed currently does not suffer from having a weak nominal anchor, but the strong nominal anchor is embodied in Alan Greenspan. Unfortunately a nominal anchor based on an indivual cannot last forever. Greenspan’s tenure at the Fed will come to an end soon and there might be some doubts that the new Chairman will be committed to the same approach, just as there were some doubts in the markets that Greenspan would be as serious about controlling inflation as his predecessor, Paul Volcker.3 Nor is there any guarantee that the relatively good
4Detailed analyses of experiences with inflation targeting can be found in Leiderman and Svensson (1995), Haldane (1995), Mishkin and Posen (1997) and Bernanke, Laubach, Mishkin and Posen (1999).
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working relationship now existing between the Fed and the executive branch, which started with the Clinton administration, will continue. In a different economic or political environment, the Fed might face strong pressure to engage in over expansionary policies, raising the possibility that time-inconsistency problem of Kydland and Prescott (1977) and Calvo (1978) may become more serious in the future. In the past, after a successful period of low inflation, the Federal Reserve has reverted to inflationary monetary policy -- the 1970s are one example -- and without an explicit nominal anchor, this could certainly happen again in the future.
WHY INFLATION TARGETING?
Inflation targeting has the potential to avoid the above problems in the Fed’s current approach. To be clear, inflation targeting involves the following five elements: 1) public announcement of forward-looking medium-term numerical targets for inflation; 2) an institutional commitment to price stability as the primary, long-run goal of monetary policy and to achievement of the inflation goal; 3) an information inclusive strategy; 4) increased transparency of the monetary policy strategy through communication with the public and the markets about the plans and objectives of monetary policymakers; and 5) increased accountability of the central bank for attaining its inflation objectives.4
Inflation targeting has many of the desirable features of the current Fed approach. It is forward looking, uses all information in deciding on the setting of policy instruments and does focus on achieving long-run price stability. However, it goes beyond the current Fed approach and this provides several advantages. First, an inflation target is readily understood by the public and is thus highly transparent. Framing the discussion of monetary policy around an inflation goal makes it easier for the Fed to communicate with the public and the markets. It can help
decrease uncertainty about future monetary policy moves, thereby decreasing market volatility. It can help focus the political debate on what a central bank can do in the long-run – that is control inflation, rather than on what it cannot do, which is permanently increase economic growth and the number of jobs through expansionary monetary policy. Thus, inflation targeting has the potential to reduce the likelihood that the central bank will fall into the time-consistency trap, trying to expand output and employment in the short-run by pursuing overly expansionary monetary policy. Indeed, inflation targeting has been able to change public debate in countries that have adopted it, with an increased focus on the long-run rather than on the short-run issue of “jobs, jobs, jobs” as in the U.S.5
Because an explicit numerical inflation target increases the accountability of the central bank, inflation targeting is also more consistent with democratic principles. Sustained success in the conduct of monetary policy as measured against a pre-announced and well-defined inflation target can be instrumental in building public support for a central bank’s independence and for its policies. The granting of operational independence to the Bank of England in 1997 illustrates this point. On May 6, 1997, the new Chancellor of the Exchequer, Gordon Brown, announced that the Bank of England would henceforth have the responsibility for setting interest rates, which previously was done by the Chancellor of the Exchequer. In the press conference, Gordon Brown explained that the inflation targeting regime justified the government’s decision: the Bank had demonstrated successful performance over time as measured against an announced clear target, and was now more accountable, making it more responsive to political oversight.
OBJECTIONS TO INFLATION TARGETING?
5See Mishkin and Posen (1997) and Bernanke, Laubach, Mishkin and Posen (1999).
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Of course not everyone sees inflation targeting positively, as is evidenced by Ben Friedman’s companion piece in this journal. There are several important objections to inflation targeting that require a response.
First, inflation targeting might be too inflexible, leading to higher output fluctuations. Ben Friedman has taken this position, especially in Friedman and Kutner (1996), in which they worry that inflation targeting might be a rigid rule that would fare as badly as Milton Friedman’s constant-money-growth-rate rule would have if it had been implemented. As Ben Bernanke and I have argued elsewhere (Bernanke and Mishkin, 1997), this is a mischaracterization of inflation targeting which can be quite flexible and is very far from a rigid policy rule. Instead, we have argued that inflation targeting is best described as “constrained discretion”.
However, the concern that inflation targeting could lead to increased output fluctuations is one that does have to be taken seriously. If a central bank solely focused on inflation control, something that Mervyn King (1996) has described as being an “inflation nutter”, then it could lead to overly high output fluctuations. However, this is not the way inflation targeting is actually practiced. I agree strongly with Larry Meyer (forthcoming) that a central bank needs to adhere to a dual mandate of the type in the Federal Reserve Act that indicates that monetary policy objectives include not only on price stability but also output stability. Indeed, the literature on optimal monetary policy typically specifies an objective function for monetary policy which puts a negative weight on both output as well as inflation fluctuations,6and operating with this type of objective function is consistent with what inflation targeting central banks have actually done.7The result has been that countries that have adopted inflation targeting have not found that output fluctuations have increased.
The argument that inflation targeting might increase output fluctuations can be turned
6For example, see the papers in Taylor (1999).
7See Bernanke, Laubach, Mishkin and Posen (1999).
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on its head. I would argue that inflation targeting can actually make it easier to reduce output fluctuations and probably has done so. First the presence of an inflation target which provides an effective nominal anchor enables a central bank to be even more aggressive in the face of negative shocks to the economy because the central bank has less fear that these moves will blow out inflation expectations. A classic example of this happened in Australia in July 1997 when the Reserve Bank of Australia lowered interest rates immediately after the currency crisis in Thailand which brought on the East Asian crisis. Despite the prospects of a substantial depreciation of the Austrailian dollar, the Reserve Bank believed that the success of their inflation targeting regime meant that inflation expectations would not rise above their targets with a monetary policy easing and thus they could ease to counter the negative demand shock arising from the deterioration in their terms of trade that was resulting from the East Asian crisis. Second, the emphasis on the floor of the inflation target range that has become a standard feature of inflation targeting in industrialized countries makes it more likely that central banks will be aggressive in combating negative shocks, so that deflationary spirals are less likely. If the Bank of Japan had an inflation target with the appropriate emphasis on the floor of the target range, then it is very likely that they would have avoided the disastrous policies pursued under the leadership of Masuro Hayami and would have been far more expansionary. Also they would have been far more likely to avoid the time-inconsistency problem outlined by Eggertsson (2003) in which the Bank of Japan was unable to commit to a long-run policy of expansion, thereby making temporary expansionary policy ineffective.
Critics of inflation targeting, most notably Don Kohn (forthcoming), who is member of the Board of Governors of the Federal Reserve, have also worried that inflation targeting may be too rigid because inflation-targeting central banks in advanced economies have often adopted a horizon for their inflation targets of two years or so, with the Bank of England being a prominent example. This can give the impression that the horizon for inflation targets is fixed, which could mean that inflation targeting will not be flexible enough. After all, models such as Svensson (1997) and
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Woodford (forthcoming) tell us that optimal monetary policy will surely adjust the target horizon and path for inflation depending on the nature and persistence of shocks. This criticism is a valid one. The use of a specific horizon like two years, which is consistent with estimates of policy lags from monetary policy actions to inflation, has not been a problem for inflation targeting in advanced economies like the United Kingdom only because inflation has not been subject to big shocks so that it has remained close to the target level. However, as Svensson (1997) demonstrates, if the inflation rate is shocked away from its long-run target, then the target horizon should be longer than the policy horizon. Although this situation has not occurred yet in advanced-economy inflation targeters, a big shock to inflation will come one day. Then for monetary policy to minimize output and inflation fluctuations optimally, the target path for inflation will have to be adjusted as it has in Brazil recently.8 This valid criticism of the fixed horizon for inflation targets does not mean that inflation targeting should not be adopted by the Fed. What it does mean is that an inflation targeting regime in the United States should make it clear, even before it is necessary, that the horizon for inflation targets needs to be flexible and will vary depending on the nature and persistence of shocks.
The second serious objection to inflation targeting is raised in Ben Friedman’s companion piece in this journal. He argues that inflation targeting will not lead to transparency because it encourages central banks to avoid discussing reduction of output fluctuations as an objective of monetary policy. I would argue that inflation targeting is not the issue here. Central bankers, whether they inflation target or not, are extremely reluctant to discuss concerns about output fluctuations. Indeed, I like to refer to the fact that central bankers care about output fluctuations but are often reluctant to talk about it as “the dirty little secret of central banking”. One remarkable manifestation of this occurred in August of 1994 at the Federal Reserve Bank of Kansas City’s Jackson Hole Conference, which is arguably the most prominent central bank conference that occurs on a regular basis. Alan Blinder, then the vice-chairman
8See Fraga, Goldfajn and Minella (2003).
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of the FOMC, had the temerity to mention that a short-run tradeoff between output and inflation exists and that therefore monetary policy should be concerned about minimizing output as well as inflation fluctuations. Blinder was then pilloried by many central bankers and in the press, with a Newsweek columnist declaring that he was not qualified to be a central banker.9 From an academic economist’s perspective, this was quite amazing since Alan Blinder didn’t say anything that was inconsistent with what our models tell us. However, it does indicate the discomfort that central bankers as a group have with discussing the role of output fluctuations in the conduct of monetary policy.
Why do central bankers have difficulty with being transparent about their concerns about output fluctuations. I have touched on this issue in an earlier article for this journal, Mishkin (2002). Central bankers interactions with the political process has shown them that when politicians talk about the need for central banks to reduce output fluctuations, politicians do not focus on the appropriate long-run tradeoff between output fluctuations and inflation fluctuations, but rather on the short-run need to create jobs. Central bankers then fear that if they agree that they should try to minimize output fluctuations as well as inflation fluctuations, politicians will use this to pressure the central bank to pursue a short-run strategy of overly expansionary policy that will lead to poor long-run outcomes. In addition, central bankers know that it is extremely difficult to measure potential output and so being forced to focus too much on output fluctuations can lead to serious policy mistakes, as it did during the Arthur Burns years at the Fed.10 The response to these problems is that central bankers engage in a “don’t ask, don’t tell” strategy which Ben Friedman rightfully criticizes.
I do think that Ben gets it exactly wrong when he criticizes inflation targeting for encouraging “don’t ask, don’t tell”. To the contrary, I believe that inflation targeting can actually help deal with the problem that Ben raises, making it easier for central bankers to be
9Samuelson (1994).
10Orphanides (2002).
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more transparent about their desire to keep output fluctuations low. Because having an inflation target makes it easier for central banks to focus on the long-run tradeoff between output and inflation fluctuations, central bankers will be more comfortable indicating that a dual mandate for monetary policy is completely consistent with pursuit of price stability Recent speeches which advocated a Federal Reserve announcement of an inflation goal by Fed governor Bernanke and former Fed governor Meyer at the Federal Reserve Bank of St. Louis conference in October 2003 did exactly this.11
Second, an inflation targeting central bank should announce that it will not try to hit its inflation target over too short a horizon because this would result in unacceptably high output losses, especially when the economy gets hit by shocks that knock it substantially away from its long-run inflation goal. Inflation targeting banks have been moving in this direction: for example, the Reserve Bank of New Zealand has modified its inflation-targeting regime to lengthen the horizon over which it tries to achieve its inflation target.12Inflation-targeting central banks can go even farther in this direction by indicating that they are ready to emulate what the Brazilians have done recently when they were faced with a substantial overshoot of their targets (Fraga, Goldfajn and Minella (2003). In January 2003, the Banco Central do Brasil announced that it was adjusting its targets upwards for 2003 from 4% to 8.5%. They also explained that getting to the non-adjusted target of 4% too quickly would entail far too high a loss of output. Specifically, the announcement indicated that an attempt to achieve an inflation rate of 6.5% in 2003 would be expected to entail a decline of 1.6% of GDP, while trying to achieve the previous target of 4% would be expected to lead to an even larger decline of GDP of 7.3%.
By announcing that they would do what the Brazilians have done if a situation arose in
11Bernanke (forthcoming) and Meyer (forthcoming)
12See Sherwin (1999), Drew and Orr (1999) and Reserve Bank of New Zealand (2000).
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which inflation were shocked subtantially away from the long-run goal, central bankers can get the dirty little secret out of the closet that they do have an appropriate concern about output fluctuations. Yet , they will still be able to assure the public that they continue to worry about the long-run and the importance of achieving price stability. In addition, as I argued above, monetary authorities can further the public's understanding that they have an appropriate concern about reducing output fluctuations by emphasizing that monetary policy needs to be just as vigilant in preventing inflation from falling too low as it is from preventing it from being too high.
CONCLUSION: THE FED SHOULD ADOPT INFLATION TARGETING
The bottom line from my commentary here is that the Federal Reserve should adopt a flexible form of inflation targeting in the near future. Although inflation targeting in the United States would probably have provided small benefits in recent years because of the superb performance of the Greenspan Fed and the tremendous credibility that Alan Greenspan has achieved, now is not the time to be complacent. It is time to make sure that the legacy of the Greenspan Fed of low and stable inflation is maintained. Adopting an inflation target is the best way for the Fed to do this.
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References
Alesina, Alberto, and Lawrence H. Summers. 1993. "Central Bank Independence and Macroeconomic Performance: Some Comparative Evidence."Journal of Money, Credit, and Banking 25, no. 2 (May): 151-62.
Bernanke, Ben S. Forthcoming. “Panel Discussion: Inflation Targeting,” Federal Reserve Bank of St. Louis, Review.
Bernanke, Ben S., and Frederic S. Mishkin. 1997. "Inflation Targeting: A New Framework for Monetary Policy?" Journal of Economic Perspectives 11, no. 2 (spring): 97-116.
Bernanke, Ben S., Laubach, Thomas, Mishkin, Frederic S. and Adam S. Posen (1999). Inflation Targeting: Lessons from the International Experience (Princeton: Princeton University Press).
Calvo, Guillermo, “On the Time Consistency of Optimal Policy in a Monetary Economy”, Econometrica, 1978, 46.
Cukierman, Alex. 1992.Central Bank Strategy, Credibility, and Independence: Theory and Evidence. Cambridge: MIT Press.
Eggertsson, Gautti B. 2003 "How to Fight Deflation in a Liquidity Trap: Committing to Being Irresponsible," IMF Working Paper. Washington: International Monetary Fund.
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Fischer, Stanley. 1994. "Modern Central Banking." In Forrest Capie, Charles A. E. Goodhart, Stanley Fischer, and Norbert Schnadt,The Future of Central Banking: The Tercentenary Symposium of the Bank of England, 262-308. Cambridge: Cambridge University Press.
Fraga, Arminio, Goldfajn, Ilan and Andre Minella. 2003. “Inflation Targeting in Emerging Market Economies,” NBER Macroeconomics Annual.
Friedman, Benjamin M., and Kenneth Kuttner. 1996. "A Price Target for U.S. Monetary Policy? Lessons from the Experience with Money Growth Targets." Brookings Papers on Economic Activity, no. 1: 77-125.
Goodfriend, Marvin. 1993. “Interest Rate Policy and the Inflation Scare Problem: 1979-1992.”Federal Reserve Bank of Richmond Economic Quarterly 79, no. 1 (Winter): 1-24.
Goodfriend, Marvin. forthcoming. “Inflation Targeting in the United States,” in Ben Bernanke and Michael Woodford, editors, Inflation Targeting (Univeristy of Chicago Press for the NBER: Chicago).
Haldane, Andrew G., ed. 1995. Targeting Inflation. London: Bank of England.
King, Mervyn (1996). "How Should Central Banks Reduce Inflation?- Conceptual Issues," in Achieving Price Stability, Federal Reserve Bank of Kansas City, Kansas City, MO: 53-91.
Kohn, Donald L. Forthcoming. “Panel Discussion: Inflation Targeting,” Federal Reserve Bank of St. Louis, Review.
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Kydland, Finn, and Edward Prescott. 1977. "Rules Rather than Discretion: The Inconsistency of Optimal Plans." Journal of Political Economy 85, no. 3 (June): 473-92.
Leiderman, Leonardo, and Lars E. O. Svensson. 1995. Inflation Targeting. London: Centre for Economic Policy Research.
Laurence H. Meyer, forthcoming. “Practical Problems and Obstacles to Inflation Targeting,”Federal Reserve Bank of St. Louis, Review.
Mishkin, Frederic, 2000. "What Should Central Banks Do?" Federal Reserve Bank of St. Louis Review, vol. 82, #6 (November/December: 1-13.
Mishkin, Frederic S. 2002. "The Role of Output Stabilization in the Conduct of Monetary Policy," International Finance, Vol. 5, #2 (Summer): 213-227.
Mishkin, Frederic S. and Adam S. Posen, 1997. "Inflation Targeting: Lessons from Four Countries," Federal Reserve Bank of New York, Economic Policy Review, vol. 3, #3 (August 1997): 9-110
Orphanides, Athanasios (2002), "Monetary Policy Rules and the Great Inflation," American Economic Review, 92(2) (May): 115-120.
Posen, Adam S. 1995. “Declarations Are Not Enough: Financial Sector Sources of Central Bank Independence.” In Ben S. Bernanke and Julio J. Rotemberg, eds., NBER Macroeconomics Annual, 1995, 253-74. Cambridge: MIT Press.
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Samuelson, Robert, 1994. “Economic Amnesia,” Newsweek, Sept. 12: 52.
Svensson, Lars.E.O., 1997. "Inflation Forecast Targeting: Implementing and Monitoring Inflation Targets," European Economic Review, 41: 1111-1146.
Taylor, John. 1999. Editor, Monetary Policy Rules (University of Chicago Press
for the NBER: Chicago).
Woodford, Michael. Forthcoming. “Inflation Targeting: A Theoretical Perspective” Federal Reserve Bank of St. Louis, Review.
Woodward, Bob. 2000 Maestro: Greenspan’s Fed and the American Dream (Simon and Schuster: New York).
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初中英语情态动词之shall和should的正确用法 相信很多同学对于shall和should的用法比较容易搞混，下面是小编为您收集整理的shall和should的正确用法，供大家参考! 初中英语情态动词之shall和should的正确用法 1、shall的用法 (1)shall用于第一、三人称陈述句中，表示说话人征求对方的意见或向对方请示。 (2)shall用于第二、第三人称陈述句中，表示说话人给对方的命令、警告、允诺或威胁。 (3)用于所有人称，表示规章、法令、预言等，可译为必须。 2、should的用法 (1)表示义务、责任或劝告、建议、命令等，意为应该。 (2)表示有一定根据的推测、推论或可能性，意为可能，该(肯定的语气没有must表推测时强)。 (3)多用于疑问句中，表示惊讶、难以相信或不应该的事。 (4)ought to和should的比较 A、ought to也可以表示推论、可能性，和should用法一样。 B、在省略回答中，ought to中的to可以省略。 C、should和ought to表示做正确的事情或理应做的事情。 be supposed to 意为被期望，应该，表示被期望发生或根据安
排、要求做某事，或认为做某事是正常的。 英语语法速记口诀大汇总 一、冠词基本用法 【速记口诀】 名词是秃子，常要戴帽子， 可数名词单，须用a或an， 辅音前用a，an在元音前， 若为特指时，则须用定冠， 复数不可数，泛指the不见， 碰到代词时，冠词均不现。 【妙语诠释】冠词是中考必考的语法知识之一，也是中考考查的主要对象。以上口诀包括的意思有：①名词在一般情况下不单用，常常要和冠词连用;②表示不确指的可数名词单数前要用不定冠词a 或an，确指时要用定冠词the;③如复数名词表示泛指，名词前有this，these，my，some等时就不用冠词。 二、名词单数变复数规则 【速记口诀】 单数变复数，规则要记住， 一般加s，特殊有几处： /t?蘩/、/?蘩/、/s/结尾，es不离后， 末尾字母o，大多加s， 两人有两菜，es不离口，
情态动词should的用法 情态动词should和can ，may ，must一样，没有人称和数的变化，有词意，但都不能单独作谓语，必须和后面的动词原形一起构成谓语。基本意思是“应当，应该”，常用来表示建议或命令等。如： You should work harder. 你应该更努力地工作。 否定式和疑问式的构成与can ，may ，must一样。如： You shouldn’t play soccer in the street.你们不应该在街上踢足球。 Who should pay the taxi driver? 谁应该付出租车钱？ 注意： 常用句型You should /shouldn’t do sth 表示“建议某人（不）做某事”。其他表示“建议”的句型还有：Why not do sth? /Why don’t you do sth? /How about doing sth? /What about doing sth? /It’s a good idea to do sth /You’d better do sth等。 should作为情态动词用，常常表示意外、惊奇、不能理解等，有“竟会”的意思，例如： How should I know? 我怎么知道？ Why should you be so late today? 你今天为什么来得这么晚？ should有时表示应当做或发生的事，例如： We should help each other.我们应当互相帮助。 我们在使用时要注意以下几点： 1. 用于表示“应该”或“不应该”的概念。此时常指长辈教导或责备晚辈。例如： You should be here with clean hands. 你应该把手洗干净了再来。 2. 用于提出意见劝导别人。例如： You should go to the doctor if you feel ill. 如果你感觉不舒服，你最好去看医生。 3. 用于表示可能性。should的这一用法是考试中常常出现的考点之一。例如： We should arrive by supper time. 我们在晚饭前就能到了。 She should be here any moment. 她随时都可能来。 1. We _________ keep the new traffic law(交通法). A. may B. should C. can D. need 2.I’d like to buy a new shirt , but I don’t know __________ . A. where could buy it B. I should take which C. which I should take D. where can I get it 写出同义表达 Why not have a rest? (1) Why _______ ________ have a rest? (2) You’d _________ _________ a rest. (3) You _______ ________ a rest. (4) ________ _________ having a rest?
shall的情态动词用法 1. 在疑问句中用于征求对方意见，主要用于第一人称(在英国英语中，也用于第三人称)，其意为“要不要”、“…好吗”。 如： Shall we meet again tonight? 咱们今晚要不要再碰碰头? Shall they wait for you? 要不要他们等你? 2. 在陈述句中表示说话者的允诺、告诫、威胁、命令、规定、必然性等，主要用于第二、三人称。 如： You shall suffer for this. 你会为此事吃苦头的。(表威胁) That day shall come. 那一天一定会来。(表必然性) You shall hear everything directly you come. 你一来就可听到所有情况了。(表允诺) 【注意】用于第一人称，则表示决心。 如： I shall return. 我一定回来。(表示决心) 好啦，今天的课程就到这里了，see you tomorrow ！ 1. 用于疑问句 shall在疑问句中可用于征求对方意见，主要用于第一人称，其意为“要不要”“……好吗”。如： Shall I turn on the light? 要不要把灯开开? Shall we take a taxi? 我们乘出租汽车，好吗? What shall I do with your mail? 我应该怎么处理您的信件? 在英国英语中也可用于第三人称。如： Shall the boy come at once? 要不要这孩子马上来? 2. 用于陈述句 shall在陈述句表示说话者的允诺、告诫、威胁、命令、规定、必然性等，主要用于第二、三人称。如： You shall have a sweet. 你会吃到一块糖。(表允诺) You shall do as you please. 你可以随意行事。(表允诺) He shall suffer for this. 他将为此受苦。(威胁) Each competitor shall wear a number. 每个参赛者要戴一个号码。(表规定)
情态动词s h a l l的用 法
情态动词shall的用法? 解答 shall 的用法如下： 在陈述句中表示说话者给对方的承诺、决心、警告、威胁等.如： I shall write to you again at the end of the month.月底我再给你 写封信. You shall have it back next week.下星期一定还你. He shall stay in bed.他必须躺在床上. ■表示强制,用于法令、条约、规章中,意为“必须,应该”.如： Candidates shall remain in their seats until all the papers hav e been collected.试卷完全收回后,应试人才能离开座位. ■在主语是第一、三人称的疑问句中征求对方意见：要不要……?……好 吗?如： Shall I turn on the lights?我开灯好吗? Shall he wait for you outside?要不要他在外面等你? ■表示不可避免的某事：一定 That day shall come.那一天总会来的.
1.(陈述句中，用于第一人称,表示将来)将,会 (表将来时时,should是shall的过去式) I shall be thirty next year. 明年我就三十岁了。 I shall go to shanghai 我将会去上海。 2.(用于陈述句中的第二、第三人称,表示说话人的意图、允诺、警告、命令、决心等)必须,应,可 You shall have it back next week. 下星期一定还你。 He shall stay in bed. 他必须躺在床上。 He says he won't go, but I say he shall. 他说他不去,但我说他必须去。 3.(用在问句中表示征求对方意见,主要用于第一、第三人称)...好吗?要不要...? Shall we begin now? 我们现在开始好吗? Shall I wait outside? 我在外面等好吗? Shall I turn on the lights? 我开灯好吗? Shall he need a glass of water? 他需要来杯水吗？ 4.(用在条约、规章、法令等文件中表示义务或规定,一般用于第三人称)应,必须 Intruders shall be punished.
一、情态动词should的用法 情态动词should有自己的意义，但不能单独作谓语，只能和其他动词一起构成谓语，表示说话人的态度或看法，后接动词原形。常见用法有以下几点： 1.表示劝告、建议等，意为“应该”，常指根据常理认为对的事或应该去做的事。 当劝某人做或不做某事时，常用“should do sth.”或“shouldn't do sth.”。should 比must 和ought to 语气更加委婉。 例句:You should brush your teeth before you go to bed.你在睡觉前应该刷牙。 You shouldn't watch TV every day.你不应该每天看电视。 2.通常用来表示现在或将来的责任或义务。 例句:Children should obey their parents.孩子们应该听从他们的父母。 We should respect the old.我们应该尊敬老人。 3.表示推断，意为“应该；可能”。 例句:They should be there by now，I think.我觉得现在他们应该都已经到了。 4.用于第一人称疑问句，询问对方的意愿，表示说话人的一种谦
逊、客气、委婉的语气。 例句:Should I open the window? 我可以打开窗户吗？ What should we do now? 我们现在该干什么呢？ 5.表示某种感情色彩，意为“竟会”，常用于以how, why开头引导的特殊疑问句中。 例句:Why should you be so early today? 你今天为什么会如此早
摄像头接口分类及基础知识
一、Camera 工作原理介绍 1．结构 2．工作原理 外部光线穿过 lens 后，经过 color filter 滤波后照射到 Sensor 面上， Sensor 将从 le ns 上传导过来的光线转换为电信号，再通过内部的 AD 转换为数字信号。如果 Sensor 没有集成 DSP，则通过 DVP 的方式传输到 baseband，此时的数据格式是 RAW DATA。如果集成了 DS P， RAW DATA 数据经过 AWB、则 color matr ix、 lens shading、 gamma、 sharpness、 A E 和 de-noise 处理，后输出 YUV 或者 RGB 格式的数据。 最后会由 CPU 送到 framebuffer 中进行显示，这样我们就看到 camera 拍摄到的景象了。3． YUV 与 YCbCr ． 一般来说，camera 主要是由lens 和 senso r IC 两部分组成，其中有的 sensor IC 集成了 DSP，有的没有集成，但也需要外部 DSP 处
理。细分的来讲，camera 设备由下边几部分构成： 1） lens（镜头）一般 camera 的镜头结构是有几片透镜组成，分有塑胶透镜（Plastic)和玻璃透镜(Glass) ，通常镜头结构有：1P,2 P,1G1P,1G3P,2G2P,4G 等。 2） sensor（图像传感器） Senor 是一种半导体芯片，有两种类型：CCD（Charge Coupled Device）即电荷耦合器件的缩写和 CMOS（Co mplementary Metal-Oxide Semiconductor）互补金属氧化物半导体。Sensor 将从 lens 上传导过来的光线转换为电信号，再通过内部的AD 转换为数字信号。由于 Sensor 的每个 pi xel 只能感光 R 光或者 B 光或者 G 光，因此每个像素此时存贮的是单色的，我们称之为 R AW DATA 数据。要想将每个像素的 RAW DATA 数据还原成三基色，就需要 ISP 来处理。 注：
should的用法： should用来提出建议和忠告，后边加动词原形，否定句直接在should后边加not. 例如：I think you should eat less junk food. 我认为你应该少吃垃圾食品。 She drives a lot and she seldom walks. So I think she should walk a lot. 她经常开车，很少走路。所以我认为她应该多走路。 Students shouldn’t sp end too much time playing computer games. 学生们不应当花太多的时间玩计算机游戏。 学习向别人提建议的几种句式： （1）I think you should… （2）Well, you could… （3）Maybe you should … （4）Why don’t you…? （5）What about doing sth.? （6）You’d better do sth. 练一练 用should或shouldn’t填空 1. I can’t sleep the night before exams. You ______ take a warm shower before you go to bed. 2. Good friends ______ argue each other. 3. There is little milk in the glass. We _______ buy some. 4. They didn’t invite you? Ma ybe you ______ be friendlier. 5. I am a little bit overweight. So I think I _______ do exercises every day. 答案：1. should 2. shouldn’t 3. should 4. should 5. should
常用摄像机的分类 根据不同感光芯片划分 我们知道感光芯片是摄像机的核心部件，目前摄像机常用的感光芯片有ccd和cmos 两种： １．ccd摄像机，ccd称为电荷耦合器件，ccd实际上只是一个把从图像半导体中出来的电子有组织地储存起来的方法。 ２．cmos摄像机，cmos称为“互补金属氧化物半导体”，cmos实际上只是将晶体管放在硅块上的技术，没有更多的含义。 尽管ccd表示“电荷耦合器件”而cmos表示“互补金属氧化物半导体”，但是不论ccd或者cmos对于图像感应都没有用，真正感应的传感器称做“图像半导体”，ccd和cmos传感器实际使用的都是同一种传感器“图像半导体”，图像半导体是一个p n结合半导体，能够转换光线的光子爆炸结合处成为成比例数量的电子。电子的数量被计算信号的电压，光线进入图像半导体得越多，电子产生的也越多，从传感器输出的电压也越高。 因为人眼能看到1lux照度（满月的夜晚）以下的目标，ccd传感器通常能看到的照度范围在0.1~3lux，是cmos传感器感光度的3到10倍，所以目前一般ccd摄像机的图像质量要优于cmos摄像机。 cmos可以将光敏元件、放大器、a/d转换器、存储器、数字信号处理器和计算机接口控制电路集成在一块硅片上，具有结构简单、处理功能多、速度快、耗电低、成本低等特点。cmos摄像机存在成像质量差、像敏单元尺寸小、填充率低等问题，1989年后出现了“有源像敏单元”结构，不仅有光敏元件和像敏单元的寻址开关，而且还有信号放大和处理等电路，提高了光电灵敏度、减小了噪声，扩大了动态范围，使得一些参数与ccd摄像机相近，而在功能、功耗、尺寸和价格方面要优于ccd，逐步得到广泛的应用。cmos传感器可以做得非常大并有和ccd传感器同样的感光度，因此非常适用于特殊应用。cmos传感器不需要复杂的处理过程，直接将图像半导体产生的电子转变成电压信号，因此就非常快，这个优点使得cmos传感器对于高帧摄像机非常有用，高帧速度能达到400到100000帧/秒。 按输出图像信号格式划分 模拟摄像机 模拟摄像机所输出的信号形式为标准的模拟量视频信号，需要配专用的图像采集卡才能转化为计算机可以处理的数字信息。模拟摄像机一般用于电视摄像和监控领域，具有通
must. (表示必要、命令或强制)必须,得 You mustn't talk like that. 你可不能这样说话。 You must do as you are told. 你必须遵嘱行事。 We must be home by six. 我们必须在六点以前回家。 2. (表示肯定的推测)一定是,谅必,八成 This must be your room. 这一定是你的房间了。 He must be eighty now. 他现在很可能有八十岁了。 3. (表示不可避免性)必然要,必定会 All men must die. 人总有一死。 4. (表示主张)一定要,坚持要 If you must go, at least wait till the rain stops. 如果你坚持要走,至少也要等雨停了再走。 5. (表示与说话人愿望相反)偏要 The machine must break down at this busy hour. 正忙的时候机器偏偏坏了。n.[S] 1. 必须做的事;不可少的事物 A walking stick is a must for me now. 如今我行走离不开手杖了。 2. 一定要看(或听、读)的东西 a. 1. 绝对必要的,必须的[B] Shall 1. (shall的过去式,表示过去将来)将 We hoped that we should be able to do that.我们希望我们能这样做。 2. (表示语气较强的假设)万一,竟然 If the car should break down on the way, you would have to walk back. 万一汽车中途抛锚,你就得走回来。 3. (表示可能性、推测、推论或期待)可能,该 She should be here any minute.她该马上就到。 Dinner should be ready by now.此刻晚饭应该做好了。 4. (表示义务、责任)应该,应当 You should do as she says.你应当照她说的去做。 He should work harder.应该更加努力。 You should help your mother with the housework.你应该帮你母亲做家务。 5. (表示委婉、谦逊)可,倒 6. (表示感情、意志等)竟然会;应该 I'm sorry it should be this way.很遗憾,事情竟会是这个样子。 It's strange that he should be absent.真奇怪,他竟会缺席。 You shouldn't have told him about it.你不该把这件事告诉他的。 7. (表示建议、命令、决定等)应该,必须 Crime should be punished.犯罪应受惩罚。 8. (表示目的)会,可以 He stood away so that we should enter the room first.他让开一步,让我们先进屋。 9. (表示结果、意愿等)就,该
摄像机类型与功能 电视监控系统的前端设备主要包括了：摄像机、镜头、云台、防护罩、支架、控制解码器、射灯等； 1：摄像机的选择 如果监视目标照度不高，对监视图像清晰度要求较高时，宜选用黑白CCD摄像机； 如果要求彩色监视时，因考虑加辅助照明装置或选用彩色�；黑白自动转换的CCD摄像机，这种摄像机当监视目标照度不能满足彩色摄像机要求时自动转化黑白摄像。 1>彩色摄像机：适用于景物细部辨别，信息量一般是黑白摄像机的10倍 2>黑白摄像机：适用于管线不住地区及夜间无法安装照明设备的地区 2：摄像机功能和工作原理 1>分辨率：表示摄像机分配率图像细节的能力，通常用电视线TVL表示，黑白摄像机水平清晰度一般选择450TVL左右； （1）25万像素左右，彩色分辨率为330线、黑白分配率420线左右的低档型； （2）25~38万像素之间，彩色分配率为420线，黑白分配率在500线上下的中档型 （3）38万以上，彩色分配率大于或者等于480线、黑白分配率，570线以上的高分配率2>灵敏度：在镜头光圈大小一定的情况下，获取规定信号电平所需要的最低靶面照度。 （1）普通型：正常工作所需照度为1~31 ux （2）月光型：正常工作所需照度为 0.1 lux左右 （3）星光型：正常工作所需照度为0.01 lux以下 （4）红外照明型：原则上可以为零照度，采用红外光源成像 3>信噪比：视频信号电平与噪声平之比，衡量摄像机质量的重要指标； 信噪比越高，图像越干净，质量就越高，通常在45~55dB之间； 4>工作温度：-10~+50dB是绝大多数摄像机生产厂家的温度指标 5>电源电压：国外摄像机交流电压适应范围是198~264V抗电源电压变化能力较强，国内摄像机交流电压适应范围一般是200~240，抗电源电压变化能力较弱；
1. 表将来时时,should是shall的过去式 2. should可用来表示推测. 3. shall可用于第一/第三人称疑问句中,表示请求许可. 4. shall可用于第二/第三人称陈述句中,表示警告/许诺/命令/威胁/规定等语气. 5. should have done sth/should not have done sth表责备语气 6. should可以表示劝告,建议语气,"应该/应当" 7. should可以用在虚拟语气中,有时可以省略;有时不可以省略,表示"万一" 8. should可以表示"居然/竟然",有不相信/惊愕的含义 1.使用shall 及 will 的传统规则规定了一个十分复杂的使用形式，其形式的含义根据主语人称而改变。在第一人称中，shall 用于表示简单的未来事件 2.在第二人称及第三人称中，同样的未来事件意义由will 表达 3.单词will 在第一人称及 shall 在用于第二、三人称时，根据上下文可能表达的决定、承诺、义务或允许这样。这样I will leave tomorrow 这句话表明说话者决定离开 You and she shall leave tomorrow 则特别象是一个命令 4.在美国，will 被用来表达在英国用法中大多为 shall 保留的含义，而shall 则限于第一人称疑问句式的提议 5.Shall 也用在正式文体中表示明确职责 Hi, my dear friends!Welcome to “Grammar Focus”! Now, let's go and see the content （内容） in it. shall 既是助动词也是情态动词，具体用法如下： 1. 助动词shall 的用法 shall + 动词原形表示一般将来时 [例] I shall study harder at English. 我将更加努力地学习英语。 We shall read some more books. 我们将读更多的书。 注：在将来时中，will 常用于第一、二人称，但shall 只用于第一人称，如果用于第二、三人称，就失去助动词的意义，变为情态动词了。 2. 情态动词shall的用法。 （1）表示说话者的意图、允许、警告、命令、决心等，用于陈述句的第二、三人称中，有“必须”之意。 [例] You shall do your homework. 你必须做你的家庭作业。 He shall listen to the music. 他应该听音乐。
第17练情态动词should的用法 1. As middle school students, we_____ fllw the public nules whereverwe go. A. would B. should C. might D. could 2. Ants are pretty small. You might think that they______ be rather weak. But what you might not know is that ants are actually very strong for their size. A. need B. can’t C. must 3.We don’t alow taking magazines out, butyou____ copy the article you needon the machine over there. A. can B. must C. should D. would 4. -- Mum may I go to see a film with my cousin? -- You______ go if you have finished your homework. A. must B. need C. should D. can 5.According to the notice, guests at this hotel____ _use the sports center at no extra cost. A. can B. should C. must D. need 6.---Mum, it’s too hot.__ I swim in the lake? ---No, you That’s too dangerous! A. Should; can’t B. Need; mustn’t C. Must; needn’t D. Could; mustn’t 7.- -The expeniment semns difiult. Would yourmind doing it for me? ---Why not do it by yoursel? I____ show you how to do it if necessary. A.can B. needn’t C. must D. shouldn’t 8.Dog___ run though soccer games at the park. It’s dangerous. A. should B. shouldn’t C. need D. needn’t 9.When a virus comes into our body, we get ill The same thing_____also happen to a computer. A. should B. need C. can D. must 10- Look! The man at the school gate____be our headmaster. He is always standing there to welco
安防摄像头6mm与3mm镜头的差异 差异肯定是有的，具体如下： 摄像机镜头是视频监视系统的最关键设备，它的质量（指标）优劣直接影响摄像机的整机指标，因此，摄像机镜头的选择是否恰当既关系到系统质量，又关系到工程造价。 镜头相当于人眼的晶状体，如果没有晶状体，人眼看不到任何物体；如果没有镜头，那么摄像头所输出的图像就是白茫茫的一片，没有清晰的图像输出，这与我们家用摄像机和照相机的原理是一致的。当人眼的肌肉无法将晶状体拉伸至正常位置时，也就是人们常说的近视眼，眼前的景物就变得模糊不清；摄像头与镜头的配合也有类似现象，当图像变得不清楚时，可以调整摄像头的后焦点，改变CCD芯片与镜头基准面的距离（相当于调整人眼晶状体的位置），可以将模糊的图像变得清晰。由此可见，镜头在闭路监控系统中的作用是非常重要的。工程设计人员和施工人员都要经常与镜头打交道： 设计人员要根据物距、成像大小计算镜头焦距，施工人员经常进行现场调试，其中一部分就是把镜头调整到最佳状态。 1、镜头的分类 按外形功能分按尺寸大小分按光圈分按变焦类型分按焦距长矩分球面镜头1 ” 25mm自动光圈电动变焦长焦距镜头 非球面镜头手动变焦标准镜头 针孔镜头固定焦距xx 鱼眼镜头 (1)以镜头安装分类所有的摄象机镜头均是螺纹口的，CCD摄象机的镜头安装有两种工业标准，即C安装座和CS安装座。两者螺纹部分相同，但两者从镜头到感光表面的距离不同。
C安装座： 从镜头安装基准面到焦点的距离是 17.526mm。CS安装座： 特种C安装，此时应将摄象机前部的垫圈取下再安装镜头。其镜头安装基准面到焦点的距离是 12.5mm。如果要将一个C安装座镜头安装到一个CS安装座摄象机上时，则需要使用镜头转换器。 (2)以摄象机镜头规格分类摄象机镜头规格应视摄象机的CCD尺寸而定，两者应相对应。 即摄象机的CCD靶面大小为1／2英寸时，镜头应选1／2英寸。摄象机的CCD靶面大小为1／3英寸时，镜头应选1／3英寸。摄象机的CCD靶面大小为1／4英寸时，镜头应选1／4英寸。如果镜头尺寸与摄象机CCD靶面尺寸不一致时，观察角度将不符合设计要求，或者发生画面在焦点以外等问题。 (3)以镜头光圈分类镜头有手动光圈（manualiris）和自动光圈（autoiris）之分，配合摄象机使用，手动光圈镜头适合于亮度不变的应用场合，自动光圈镜头因亮度变更时其光圈亦作自动调整，故适用亮度变化的场合。自动光圈镜头有两类： 一类是将一个视频信号及电源从摄象机输送到透镜来控制镜头上的光圈，称为视频输入型，另一类则利用摄象机上的直流电压来直接控制光圈，称为DC 输入型。自动光圈镜头上的ALC（自动镜头控制）调整用于设定测光系统，可以整个画面的平均亮度，也可以画面中最亮部分（峰值）来设定基准信号强度，供给自动光圈调整使用。一般而言，ALC已在出厂时经过设定，可不作调整，但是对于拍摄景物中包含有一个亮度极高的目标时，明亮目标物之影像可能会造成"白电平削波"现象，而使得全部屏幕变成白色，此时可以调节ALC来变换画面。另外，自动光圈镜头装有光圈环，转动光圈环时，通过镜头的光通量会发生变化，光通量即光圈，一般用F表示，其取值为镜头焦距与镜头通光口径之比，即：
情态动词shall,should,ought to用法 一、shall 的用法 1.在疑问句中用于征求对方意见，主要用于第一人称(在英国英语中，也用于第三人称)，其意为“要不要”、“…好吗”。如： Shall we meet again tonight? 咱们今晚要不要再碰碰头? Shall they wait for you? 要不要他们等你? 2.在陈述句中表示说话者的允诺、告诫、威胁、命令、规定、必然性等，主要用于第二、三人称。如：You shall suffer for this. 你会为此事吃苦头的。(表威胁) That day shall come．那一天一定会来。(表必然性) You shall hear everything directly you come. 你一来就可听到所有情况了。（表允诺） 注：用于第一人称，则表示决心。如 I shall return. 我一定回来。(表示决心) 二、should 和 ought to 的用法 1.表示均表示“应该”、“按理应当”，有时可互换，只是 ought to 语气更重，较多地反映客观，should 则强调主观看法，用于条件句表示“万一”，还有“竟然”之意。 2.谈论现在的情况，后接动词原形；谈论正在进行的情况，后接动词的进行式；谈论过去的情况，后接动词的完成式。如： He ought not to [should not] do that. 他不应当这样做。 You should [ought to] be listening. 你应该听才对。
He should [ought to] arrived by now. 到现在他们应该已经到了。 3.有时表示推测，语气较肯定，通常是指非常可能的事(因为暗示有一定的事实依据或合乎常理)，而与之相比，may, might, could 等则相对较弱，尤其是 might, coul d。请看1998年一道高考题： “When can I come for the photos? I need the m tomorrow afternoon.” “They _____ be ready by 12:00.” A. can B. should C. might D. need 在四个备选项中，A、B和C均表示推测，但A通常不用于肯定句中表示推测，故不宜选；B和C虽均可用于肯定句表示推测，但根据对话情景顾客下午要照片，如果店主中午12点还不能把照片冲洗出来，那么生意肯定难做成，所以店主应用肯定语气较强的should(=应该)来回答顾客，而不是用语气较弱的might(=有可能)，即应选B 不选C；至于选项D，它作为情态动词通常不用于肯定句，不能选。
表示“应该”和“必须”的情态助动词should, ought to, have to 与must （1）表示不可逃避的义务或表示“必须”的must。must通常只用于现在时和将来时，其他时态则用have to代替。have to比must往往更强调客观的要求或外在的原因： In the play, she must appear in a bright red dress and long black stockings. 演出时她必须穿一条鲜红色的裙子和黑色的长筒袜。 Last year in another play, she had to wear short socks and a bright, orange-coloured dress. 去年在演另一个剧时，她不得不穿短袜和一件鲜艳的橘红色的衣服。 （2）should 和ought to都可译为“应该”，表示义务、责任或某个正确的行为。ought to 比should语气略强些，多用于肯定句；疑问句与否定结构则多用should。与它们相比，must 和have to 的语气要强得多，没有选择余地： must和have to表示“必须”，而should和ought to表示“责任”、“义务”或是“一个正确的行动”。试比较： I can’t go to the cinema tonight; I must (or have to) write some letters. 今晚我不能去看电影，我必须写几封信。（我没有选择，我必须而且将会写这些信。） I should (or ought to) do some work tonight, but I think I shall go to the cinema instead. 今晚我应当做一些工作，不过我想我会去看电影的。（对我来说，正确的做法是工作，但是我选择了去看电影。） （3）had to表示“过去的必须”，表示过去必须做某事。should be doing(应正在做)，而“should( ought to)+have+过去分词”表示过去应该做（或完成）而没有做的事，我们经常翻译为“本该做…”。 I missed the train, so I had to take a taxi.（我没有选择，只有叫计程车） I’m sorry I’m late, I should(or ought to) have taken a taxi.（我知道正确的做法应该是叫车来的，但是我没有叫。） You ought to （should）have been more careful in this experiment. 你当时在做试验时应该更仔细点。 ought to have done sth, should have done sth表示本应该做某事，而事实上并没有做。否定句表示"不该做某事而做了"。例如： He ought not to have thrown the old clothes away.他不该把旧衣服扔了。（事实上已扔了。）
情态动词shall/would/may 1. Excuse me. ______ you please pass me that cup? A. Do B. Should C. Would D. Must 参考答案：C 本题考查would的用法。“表委婉地提出请求、建议或看法”应该用情态动词would，该句的意思是“请你递给我那个杯子”，should意思是“应该”，must 意思是“必须”，均不符合句意，故正确答案为C。 2. 用括号中所给单词的适当形式完成句子。 Would you ______ cleaning the window? (mind) 参考答案：mind 情态动词would后面要用动词原形，故该空应填mind。 3. ______ you like to have another try? A. Could B. Will C. Would D. Do 参考答案：C “表委婉地提出请求、建议或看法”并且与like搭配的应该用would，故正确答案为C。 4. ______ I have a word with the teacher, sir? A. May B. Would C. Will D. Should
参考答案：A 本题考查may的用法。may表示许可或征求对方的许可，意思是“可以”，will 意思是“将要”，would意思是“愿意”，should意思是“应该”，而句意是“先生，我可以和这位老师说几句吗”，故正确答案为A。 5. - May I talk about it with anyone I like? - No, you ______ . A. shouldn’t B. mustn’t C. needn’t D. don’t have to 参考答案：B 回答may开头的疑问句，否定回答的结构有“No, you can’t”、“No, you mustn’t”、“No, you’d better not”，故该题正确答案为B。 6. - ______ I visit Lucy on Sunday, Mum? - Yes, you ______ . A. Must; can B. Need; need C. May; may D. May; need 参考答案：C 问句的意思是“妈妈，我周日可以去拜访Lucy吗”，因此应该用may，回答may 开头的疑问句，肯定回答结构应该用yes, you may，故该题正确答案为C。 7. - May I go now? - No, you ______ . You ______ stay here. A. needn’t; have to B. nee dn’t; must C. mustn’t; has to
专题归类复习一 情态动词should与could的用法 ●语法讲解 1．should是情态动词shall的过去式，但有时并不表示过去。(1)表示委婉的劝告或建议，意为“应该”。如： You should hand in your composition at once. 你应该立刻交上你的作文。 (2)表示可能性或推断，意为“可能；应该”。如： I think they should be there now. 我想他们现在应该在那里。 (3)用于特殊疑问句中，表示意外、惊奇、不能理解等强烈感情。如：How should you know that? 你是怎么知道那件事的？ What should you do to relax? 你该做什么来放松呢？ 2．could是情态动词can的过去式，但有时并不表示过去。 (1)表示提议，比can更客气、委婉。 I could do the shopping for you, if you are tired. 如果你累了，我能帮你买东西。 (2)表示请求，语气比can更客气、委婉。 Could you show me the way to the hospital? 你能告诉我去医院的路吗？ ●语法精练 Ⅰ.单项选择 ( ) students at least one hour a day for sports. A．would B．might C．should D．could ( ) tell me how to get to the post office? A．Must B．Need C．Could D．Should ( )3.—When can I come for the photos? I need them tomorrow afternoon. —They________be ready by 12：00. A．can B．should C．might D．need ( )4.—Could I borrow your dictionary? —Of course you________． A．can B．must C．should D．will ( ) loves playing basketball.