# “Of” and “For” Before “-ing”

What are the rules for choosing whether to use "of" or "for" before a word ending in "-ing?"

Example:

We propose a method of simplifying algebraic expressions.
We propose a method for simplifying algebraic expressions.

I have seen it written both ways, and would like to know which way is proper. Or is this a case where "it depends?"

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You have been ill-informed. The preposition choice is governed by the preceding word -- the word the prepositional phrase modifies -- and not by the object of the preposition. And every word has its own rule. Therefore there can be no rules of the sort you request. – John Lawler Mar 29 '12 at 14:21
@John Lawler: Yes - it just so happens that method can be followed by both of and for equivalently in many contexts. If it had been way then of would be favoured (as opposed to technique, where for wins out). – FumbleFingers Mar 29 '12 at 16:40

The choice of preposition has less to do with the following gerund (-ing word; in your example, the word simplifying) than with the word method. It appears from the following NGram (corpus English, 1800 to 2008) that "method of" is much more commonly used than "method for." I think both are understandable, however, and both are used.

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It's not a simple matter of "always use 'of' before a word ending in -ing" or "always use 'for' ...". It depends on the context of the whole sentence. It would depend more on the word that precedes the "of" or "for" than on the word that follows. Like you would write, "What is your reason FOR doing that?" but "What is the result OF doing that?"

"Of" and "for" have fairly similar meanings. I'm trying to think of a general rule about when you use either. "Of" generally means "belonging to" while "for" means "related to the purpose of". For example, "book of mine" means the book I own. "Book for math class" means a book intended to be used in math class. But there are so many shades and ranges of meaning that this is really inadequate. I fear you have to take them case by case.

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Both of these statements are grammatical.

"For" would be more common. I think that "method of" is idiomatic, and in general wouldn't be correct. An example of the more general case where this won't work is "I'm collecting pictures for testing colour recognition by children" and "I'm collecting pictures of testing colour recognition by children", which have contradictory meanings. (The first means pictures to be used in the tests as opposed to pictures of the test taking place.)

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Your "I think..." sentence seems jumbled. The example given has nothing to do with "method of". Also, "method of" is not so much an idiom ("An expression peculiar to or characteristic of a particular language, especially when the meaning is illogical or separate from the meanings of its component words") as straightforward language. – jwpat7 Mar 29 '12 at 17:01
I believe "method of" is idiomatic, for the reason stated above. See also JLG's answer. I have, however, tidied up the language to make the meaning clearer as you suggest. The example is of necessity somewhat contrived, as I wanted a sentence that had a similar grammatical construction to the poster's sentence. – Christi Mar 30 '12 at 1:32