一句话 时态

past过去以往之前

S

Tom was a good boy.      以前是

Tom used to be a good boy.      曾经是（与现在不是了形成对比）

C

Tom was being a good boy at this time yesterday

P

Tom  had been  a good boy before he got to know Mr. Zhao.之前一直是（后来不是了）

PC

Tom  had been being a good boy if his father stayed home last september.

future未来将来以后

Tom will(I shall)  be a good boy.      将会是（客观必然性）

         Tom seems to be a good boy.     （seem 和same同源）有迹象表明是

Tom appears to be a good boy.      （只从表面看来）貌是

Tom is going（wants/hopes/wishes/decides/plans）to be a good boy.打算成为（主观）

Tom will be being a good boy at this tomorrow.

Tom will have been a good boy for days by next september.

Tom will have been being a good boy for days while his fatherstays home next september.

一句话时态

present现在

simple

Tom is a good boy.      现在是

Tom must  be a good boy.      一定是（肯定推测）

         Tom can(not) be a good boy.（迹象或经验表明）可能（不可能）是

Tom may be a good boy.      也许是（不充分肯定）

continuous

Tom is being a good boy these days.

perfect

Tom has been a good boy.一直是/已经是（强调时间段）

PC(完成进行)

Tom has been being a good boy since last year.

past-future过去将来（组合）

Tom  could/would/should/might/ be（become） good boy. 状态（动作）

Tom would be being a good boy for days if his father stayed home last september.

Tom would have been  a good boy if he hadn't met Mr. Zhao.（如果.......）现在就依然是（实际不是）

虚拟倒装

 Hadn't  he met Mr. Zhao，Tom would have been a good boy . （如果.......）现在就依然是（实际不是）

Tom couldn‘t /wouldn't /shouldn't/needn't have been a good boy if he had met Mr. Zhao.      

Tom would have been being a good boy for days if his father had stayed home next september.