情态动词表推测怎么选：must一定 can't不可能 may/might可能，找依据定语气三步法
引言
情态动词表推测是中考选择题的高频坑：题干给线索，选项给 must、can't、may、might。只要按"找依据→定语气→选答案"三步走，这类题就能秒判。
核心概念：四个词对应四种把握程度
```text
must be = 一定是（肯定推测，把握最大，只用于肯定句）
may be = 也许是（肯定推测，把握较小）
might be = 也许是（把握比 may 更小）
can't be = 不可能是（否定推测，把握最大）
共同点：后面都接动词原形（be 或实义动词）
```
```text
把握程度由强到弱：
must（100% 肯定） > may > might > could（可能性最弱）
can't（100% 否定）——只用于否定推测
口诀：肯定 must，否定 can't，模糊 may/might
```
三步判断法
```text
第一步：找依据——题干里有没有给出确定线索
第二步：定语气——依据确凿→ must；依据不足→ may/might；与事实相反→ can't
第三步：选答案——核对选项
```
```text
例题：Whose notebook is this?
It ______ be Lily's. Look! Her name is on the cover.
→ 第一步：封面上写着 Lily 的名字，证据确凿
→ 第二步：肯定推测
→ 第三步：must（一定是）
```
用法细节
```text
- must 表推测只用于肯定句
He must be at home. 他一定在家。
- can't 表推测（不可能），用于否定推测
She can't be in the classroom. 她不可能在教室。
- may / might 表示把握不大的可能
It may rain tomorrow. 明天可能下雨。
He might be late. 他也许会迟到。
- can 没有肯定推测用法（不说 can be 表"可能"）
```
看依据选词
```text
His car is outside. He ______ be in the house.
→ 车在外面 → 人在屋里，线索强 → must
He often comes by car, but he ______ come by bus today.
→ 只是"经常"，今天不确定 → may
The man over there ______ be our teacher. Our teacher has gone to Beijing.
→ 老师已在北京，眼前这位不可能是他 → can't
```
实战练习
```text
- The light is on. He ______ be at home. → must
- It ______ snow tomorrow, but I'm not sure. → may/might
- She ______ be at school. She is ill today. → can't
- Look at his wet clothes. It ______ be raining. → must
```
总结
```text
must = 一定是（肯定句专用）
can't = 不可能是（否定推测）
may / might = 可能是（把握依次减弱）
can 无肯定推测用法
三步法：找依据 → 定语气 → 选答案
口诀：肯定 must，否定 can't，模糊 may/might
```
```text
今日小抄：
He must be at home. 他一定在家。
She can't be in the classroom. 她不可能在教室。
It may rain tomorrow. 明天可能下雨。
口诀：肯定 must，否定 can't，mustn't 是禁止
```