Modal 2 (past)

A

100

I can swim.

できた

I could swim.

200

I must get a visa. 

ねばならなかった

I had to get a visa.

300

I should study for the test.

するべきだった（後悔）

I should have studied for the test.

400

The plane should take off. (+already)

すでに離陸しているはずだったのだが

The plane should have taken off already.

B

100

I am able to swim.

できた

I was able to swim.

200

I have got to get a visa.

ねばならなかった

I had to get a visa.

300

I ought to study for the test.

するべきだった（後悔）

I ought to have studied for the test.

400

He must be sick.

病気だったに違いない。

He must have been sick.

C

100

You can pass the exam.

できた

You were able to pass the exam.

X You could pass the exam.

200

I am supposed to meet him.

会うことになっていたが、(会わなかった)

I was supposed to meet him.

300

I shouldn't watch the Youtube video.

観るべきではなかった（後悔）

I shouldn't have watched the Youtube video.

400

He may be sick.

病気だったのかもしれない

He may have been sick.