猜谜的游戏，伴随着每一个孩子的成长。今天我们就将学习在英语中如何进行推测。整节课将伴随着一个猜谜的小游戏，和同学们一起，在实际的语境中练习情态动词表示推测的用法。通过这个单元的学习，同学们将会，根据信息进行预测，推断和续写故事。所以，以后再读小说的时候，不妨试着用英语猜一猜将要发生什么事情！
Can and could
The modal verb can expresses possibility in either a dynamic, deontic, or epistemic sense, that is, in terms of innate ability, permissibility, or possible circumstance. For example:
• I can speak English means "I am able to speak English" or "I know how to speak English".
• You can smoke here means "you may (are permitted to) smoke here" (informal English may or might is sometimes considered more correct than can orcould in these senses).
• There can be strong rivalry between siblings means that such rivalry is possible.
The preterite form could is used as the past tense or conditional form of can in the above meanings (see § Past forms above). It is also used to express possible circumstance: We could be introuble here. It is preferable to use could,may or might rather than can when expressing possible circumstance in a particular situation (as opposed to the general case, as in the "rivalry" example above, where can or may is used).
Both can and could can be used to make requests: Can/could you pass me the cheese? means "Please pass me the cheese" (where could indicates greater politeness).
It is common to use can with verbs of perception such as see, hear, etc., as in I can see a tree. Aspectual distinctions can be made, such as I could see it (ongoing state) vs. I saw it (event). See can see.
The use of could with the perfect infinitive expresses past ability or possibility, either in some counterfactual circumstance (I could have told him if I had seen him), or in some real circumstance where the act in question was not in fact realized: I could have told him yesterday (but in fact I didn't). The use of can with the perfect infinitive, can have..., is a rarer alternative to may have... (for the negative see below).
The negation of can is the single word cannot, only occasionally written separately as can not.[7] Though cannot is preferred (as can not is potentially ambiguous), its irregularity (all other uncontracted verbal negations use at least two words)sometimes causes those unfamiliar with the nuances of English spelling to use the separated form. Its contracted form is can't(pronounced /kɑːnt/ in RP and some other dialects). The negation of could is the regular could not, contracted to couldn't.
The negative forms reverse the meaning of the modal (to express inability, impermissibility or impossibliity). This differs from the case with may or might used to express possibility: it can't be true has a different meaning than it may not be true. Thus can't(or cannot) is often used to express disbelief in the possibility of something, as must expresses belief in the certainty of something. When the circumstance in question refers to the past, the form with the perfect infinitive is used: he can't (cannot) have done it means "I believe it impossible that he did it" (compare he must have done it).
Occasionally not is applied to the infinitive rather than to the modal (stress would then be applied to make the meaning clear):I could not do that, but I'm going to do it anyway.
May and might
The verb may expresses possibility in either an epistemic or deontic sense, that is, in terms of possible circumstance or permissibility. For example:
• The mouse may be dead means that it is possible that the mouse is dead.
• You may leave the room means that the listener is permitted to leave the room.
In expressing possible circumstance, may can have future as well as present reference (he may arrive means that it is possible that he will arrive; I may go to the mall means that I am considering going to the mall).
The preterite form might is used as asynonym for may when expressing possible circumstance (as can could – see above). It is sometimes said that might and could express a greater degree of doubt than may. For uses of might in conditional sentences, and as a past equivalent to may in such contexts as indirect speech, see § Past forms above.
May(or might) can also express irrelevance in spite of certain or likely truth: He may be taller than I am, but he is certainly not stronger could mean "While it is (or may be) true that he is taller than I am, that does not make a difference, as he is certainly not stronger."
May can indicate presently given permission for present or future actions: You may go now. Might used in this way is milder: You might go now if you feel like it. Similarly May I use your phone? is a request forpermission (might would be more hesitant or polite).
A less common use of may is to express wishes, as in May you live long and happy or May the Force be with you (see also English subjunctive).
When used with the perfect infinitive, may have indicates uncertainty about a past circumstance, whereas might have can have that meaning, but it can also refer to possibilities that did not occur but could have in other circumstances (see also conditional sentences above).
• She may have eaten the cake (the speaker does not know whether she ate cake).
• She might have eaten cake (this means either the same as the above, or else means that she did not eat cake but that it was or would have been possible for her to eat cake).
Note that the above perfect forms refer to possibility, not permission (although the second sense of might have might sometimes imply permission).
The negated form of may is may not; this does not have a common contraction (mayn't is obsolete). The negation of might is might not; this is sometimes contracted to mightn't, mostly in tag questions and in other questions expressing doubt(Mightn't I come in if I took my boots off?).
The meaning of the negated form depends on the usage of the modal. When possibility is indicated, the negation effectively applies to the main verb rather than the modal: That may/might not be means"That may/might not-be", i.e. "That may fail to be true".But when permission is being expressed, the negation applies to the modal or entire verb phrase: You may not go now means "You are not permitted to go now" (except in rare cases where not and the main verb are both stressed to indicate that they go together: You may go or not go, whichever you wish).
