'Must have' vs 'Should have'

[Tom]

Hi

I would like to know if I could use "must have" in place have of "should have" for the sake of emphasis.

1- You should have taken your medicine.
2- You must have taken your medicine.

Tom

[Pamela]

Hi Tom
I think your two examples express different meanings
In the first sentence should is similar in meaning with ought to
In the second sentence must expresses supposition or probability.

That is how I understand your sentences.

[Yankee]

Yes, Pamela is right. The second sentence means that I have drawn the conclusion that you have taken your medicine.

The first sentence I would understand as a reproach because you have not taken your medicine.
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Amy
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ESL teacher, and native speaker of American English

[Tom]

OK and thanks! Please see below:

1- You should respect your elders.

Now I put emphasis in my red sentence,

1- You must respect your elders.

So,

1- You should have respected your elders.

Now I again put emphasis in my blue sentence,

1- You must have respected your elders.

If no, then how I am supposed to put emphasis here?

Tom

[Alan]

Hi Tom,

I don't think emphasis plays a part. As Amy has explained, 'should' has the sense of doing something morally right 'must' has a sense of 'obligation' or in the perfect form (made not from the modal 'must' because it's defective) where the 'perfect' notion is transferred to the following infinitive, suggests something is highly probable.

A
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English as a Second Language
You can read my ESL story Only Three Letters