Past deductions: I am sure they would (must) have done plenty of testing

Question

Do you agree that the commenter should have used (must) instead of (would) for making deductions. Or maybe should have dropped would and used "and I am sure they have done plenty of testing", but would not this be considered a statement and not a deduction anymore?

I have checked the topics on making deductions about past events and found none used the modal 'would'.

The comments can be found below the article entitled: Android Wear's latest update adds GPS support and offline music playback

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WhiteRAZOR

It could probably do with one [physical button] on the top or bottom without extruding too much. I don't like how this and others don't favour those who wear it on their right wrist.

Although I haven't tried the Apple Watch, and I am sure they would have done plenty of testing, I don't like the crown. Every other watch I have to take the watch off to use the crown. Maybe it isn't so tight and can be operated smoothly with one finger, unlike standard analoges [sic].

The above comment was a reply to the following, probably mistaken, critical comment of an Android Watch

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Cyber_Akuma

I know this unpopular opinion will get me lambasted, but seriously, Android Wear NEEDS to have some kind of physical button (or other physical input) support instead of being 100% touch-only (no, a single home button a-la iPhone does not count). As much as I hate to admit it, even Apple got this right and realized how stupid multi-touch and touch-only input on a 2 inch screen would be.

Answer 1

To begin with, I see dangers in trying to differentiate too strictly between a statement and a deduction. In one sense, any sentence beginning with, for example, "I am sure (that) ..." is a statement, though what the speaker is claiming to be sure about may well be a deduction.

There is also the problem of knowing how much certainty is in the speaker's mind when s/he begins a statement with "I am sure (that) ...".

We also need to remember that the degree of certainty in my mind when I say "They may have done ..." may be the same as that in your mind when you say "They will have done ..". This is particularly true in speech, when intonation can suggest a great deal.

Having said all that, it seems to me that most speakers have a similar ranking of certainties:

They have done that - seen as a fact

They will have done that - seen as a certainty

They would have done that - seen as a more doubtful certainty.

They must have done that - seen as a logical deduction.

They may have done that - seen as a possibility

They might have done that - seen as a more doubtful possibility.

(Some speakers may use 'may' and 'might' with a very similar meaning, and some may use only one of these two modals.)

That is all a rather long-winded way of saying that "They would have done ..." can assert a degree of certainty, though not, in itself, of deduction.