A
I can swim.
できた
I could swim.
I am able to swim.
できた
I was able to swim.
You can pass the exam.
できた
You were able to pass the exam.
X You could pass the exam.
I must get a visa.
ねばならなかった
I had to get a visa.
I have got to get a visa.
ねばならなかった
I had to get a visa.
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.
I should study for the test.
するべきだった（後悔）
I should have studied for the test.
I ought to study for the test.
するべきだった（後悔）
I ought to have studied for the test.
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.
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.
He must be sick.
病気だったに違いない。
He must have been sick.
He may be sick.
病気だったのかもしれない
He may have been sick.