"Used to" or "used for"? [closed]

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?

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:

The button is used to open the dialog.

The button is used for opening the dialog.

Both of these are perfectly fine and mean the same thing.

The button is used to opening the dialog.

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.

• When used to is followed by the infinitive form of the verb, it's pronounced with a voiced sibilant [yuzd] and means "employed as a tool":

  used to break the fire alarm glass

• When used for is followed by the present participle form of the verb, it's pronounced with a voiced sibilant [yuzd] and means "employed as a tool":

  used for breaking the fire alarm glass

• When used to is followed by the the present participle form of the verb, it's pronounced with a voiceless sibilant [yust] and means "is accustomed to doing something":

  used to reading binary data

When it's written down, of course, the pronunciation has to be inferred from context.

I see nothing incorrect with four of the sentences your question says are "wrong":

• The button is used [yuzd] to open the dialog.

  "as a tool" has been elided from the sentence.

• The hammer is used [yuzd] to break the glass.

  "as a tool" has been elided from the sentence.

• John is used [yuzd] to read data.

  This means only that John has one function on the job: he reads data. Just as a canary is used in a coal mine to detect deadly gas. This is not the best way to say it, of course, because it leads the reader down the garden path to the wrong interpretation and requires a second read. The only justification for this particular sentence, is seems to me, is when John is a robot of some kind or John is a prisoner of war who hasn't been executed or forced to do hard labor because he has data-reading skills that are useful to his captors. They use him and his skills.

• John is used [yuzd] for reading data.

  John is a robot data reader and "as a tool" has been elided from the sentence.