句子语义学
词和词之间有各种各样的意义关系，我们称之为sense relation。句子也一样，可以有各种意义关系。句子语义学是在句子层面对意义进行研究，并把句子当成一个整体来看待。
◆Presupposition前提/预设，这一概念是由哲学家弗雷格（G.Frege）首先提
出来的。在言语交际中，我们所说的一句句话并不是孤立的，相互之间毫无联系的。相反前一句话和后一句话往往有密切的联系。
Please open the door.
这句话的意思很清楚，就是“请把们打开”，但是说这句话必须有一个前提，那就是“现在要开的门再说话时是关着的”。
所以从语义的角度来看，句子所包含的“前提”和这个句子本身的意义有十份密切的关系
句子的前提有这样的特点：否定了句子本身，句子的前提保留不变。
John is married.
John exists.
John is not married.
◆Semantic presupposition and pragmatic presupposition
语义预设是对语句之间关系所做的逻辑分析，他面对的是一种不变的关系：即如果P在语义上预设Q, 则P总是在语义上预设Q。
但在实际的语言活动中（语用预设），预设通常不是语义中稳定的不受约束的部分。这也正是有些语言学家认为预设属于语用学而不属于语义学的主要原因。一个重要的事实是，在一定的语境里，预设会消失，也就是说预设具有可消失性(defeasibility)。例如：
Sue cried before she finished her thesis.
Sue died before she finished her thesis.
◆What is Semantic Presupposition?
In many discussions of the concept, presupposition is treated as a relationship between two propositions by the linguists. If we say the sentence in (1a.) contains the proposition p and the sentence in (1b.) contains the proposition q, then, using＞＞to mean …presupposes‟, we can represent the relationship as in (1c.).
(1) a. Mary‟s dog is cute. (＝p)
b. Mary has a dog. (= q)
c. p ＞＞q
Interestingly, when we produce the opposite of the sentence in (1a.) by negating it (= NOT p), as in (2a.), we find that the relationship of presupposition does not change. That is, the same proposition q, repeated as (2b.), continues to be presupposed
by NOT p, as shown in (2c.).
(2) a. Mary‟s dog isn‟t cute. (＝NOT p)
b. Mary has a dog. (= q)
c. NOT p ＞＞q
Presupposition is an inference（推论）to the proposition of the sentence. Take the following sentences for example again:
e.g. (3) John is married.
(4) John exists.
(5) John is not married.
Comment: if (3) is true, (4) is true; if (3) is not true, (4) is still true. In this case, we can say both (3) and (5) presuppose (4). A presupposition is something the speaker assumes to be the case prior to making an utterance. Speakers, not sentences, have presuppositions. An entailment is something that logically follows from what is asserted in the utterance. Sentences, not speakers, have entailments.
◆Semantic presupposition would be based on the following definition:
Sentence A semantically presupposes another sentence B iff:
if and only if, iff是充分必要条件
(a) in all situations where A is true, B is true
(b) in all situations where A is false, B is true
◆Types of presupposition
Potential presupposition: in the analysis of how speakers‟ assumptions are typically expressed, presupposition has been associated with the use of a large number of words, phrases, and structures. These linguistic forms shall be considered as indicators of potential presuppositions, which can only become actual presuppositions in contexts with speakers. The following kinds of presuppositions are all potential presuppositions. Now we‟ll look at the major presupposition types marked by different linguistic features.
◆Existential presupposition: presuppose the existence of something.(my). It is not only assumed to be present in possessive constructions, but more generally in any definite descriptions such as definite noun phrase with determines …the‟, …this‟, …that‟, …these‟, …those‟, etc. By using any of the expressions in (16), the speaker is assumed to be committed to the existence of the entities named.
(16) e.g. The king of Sweden, the cat, the girl next door (Yule, 2004: 27)
◆Factive presupposition: presuppose something as a fact.(know). A number of factive verbs, such as …realize‟in (17a) and …regret‟in (17b), as well as phrases involving …be‟ with …aware‟ in (17c), …odd‟ in (17d), and …glad‟ in (17e) have factive presuppositions.
(17) a. She didn‟t realize he was ill.
(＞＞He was ill)
