To me, "used to" and "used for" are incompatible, as shown in the examples below. However, I am unable to substantiate this. MS Word doesn't "see" the differences, so I turned to "Essential grammar in use" (Murphy) and "The Chicago manual of style", but still come up with nothing. And the Internet has proven totally unreliable. Please follow my reasoning:
Used ”to” or ”for”?
Google search:
"button is used for": 2,250,000 hits
"button is used to" : 3,260,000 hits
Sentences below checked in MS Word English US: (My interpretation in parentheses)
The button is used to open the dialog. (Wrong)
The hammer is used to break the glass. (Wrong)
John is used to read data. (Wrong)
The button is used for opening the dialog. (Correct) (= a tool for opening)
The hammer is used for breaking the glass. (Correct) (= a tool for breaking)
John is used for reading data. (Wrong)
The button is used to opening the dialog. (Wrong)
The hammer is used to breaking the glass. (Wrong)
John is used to reading data. (Correct) (= in the habit of reading)
Grammar check results: No corrections whatsoever – Grammar check simply doesn’t react to the above sentences, not even those that are obviously wrong.
In lieu of further guidance, I will have to rely on my own interpretation, as stated above.
Correct or wrong?
Best Answer
You seem to believe that used to is only used to indicate habitual actions, while used for is only used for indicating instrumental actions. This is only half-right. While used for is restricted to instruments or tools, used to can be used with both senses. Taking a few of your examples:
Both of these are perfectly fine and mean the same thing.
This one is grammatically acceptable, though the meaning is strange because it states that the button is somehow accustomed to opening the dialog. We don't normally think of buttons having habits—but aside from that, there's nothing wrong with the grammar.
Note that habitual used to is pronounced somewhat differently from instrumental used to. The habitual is pronounced as a single word with highly reduced "to", approximately [justə]. The instrumental is not so completely reduced, the coda of "used" retains its voicing, and the normal lengthening of the vowel before voiced consonants occurs, giving approximately [ju:zd.tə].
As a final note, computerized grammar checkers are basically useless, and expecting MS Word or any other word processor to give you accurate grammar advice is a waste of time.