Going through Erica Meltzer’s Grammar SAT book right now and I just came across this one…
“Far from eliminating war, the new diplomatic system instituted in Europe during the early nineteenth century simple changed the reasons to fight and the methods of combat”
Here, she’s saying that “to fight” is wrong. “For fighting” may sound a bit better, but aren’t both correct? Is there something inherently wrong with the infinitive form, making the gerund required?
Thanks 
For this one, it really comes down to being good with your ear. To fight sounds weird and choppy; however if the sentence was structured like: Far from eliminating war, the new diplomatic system instituted in Europe during the early 19th century simply changed the reasons of/for fighting and the methods of combat. I know that either one would work better, but maybe you’re better off confirming this with @marvin100
Any thought @marvin100 ?
Before @marvin100 or other esteemed grammasters come to the rescue, you can peruse these elucidating pages:
http://www.englishpage.com/gerunds/noun_infinitive_list.htm
http://www.englishpage.com/gerunds/noun_prep_gerund_list.htm
http://www.englishpage.com/gerunds/infinitive_list.htm
http://www.englishpage.com/gerunds/gerund_list.htm
More of such here:
[Gerund and Infinitive Reference Lists](Gerunds and Infinitives | ENGLISH PAGE)
Out of context, there is no significant difference between “for fighting” and “to fight.”
In context, the question is really about a very subtle bit of parallelism, which is more clearly seen when you leave the parentheses to indicate the choices.
Notice that “combat” is not changeable. Notice that it’s a noun. Ideally, therefore, the phrase linked to “combat” with “and” will also contain a noun.
“Fight” is part of a phrase that can be changed, but it’s a verb, not a noun. “Fighting” is a gerund, so it’s a noun. "Of and “for” are both prepositions. That means that “for fighting” parallels “of combat” in a way that “to fight” does not. They are both preposition + noun combinations.
I’d hate to take the test where this makes the difference between a 35 and a 36.
Winnowing is done with extreme prejudice, that’s for sure.
How about this College Board pearl, in which gerund/infinitive subtleties trump parallelism:
http://talk.collegeconfidential.com/discussion/comment/13896583#Comment_13896583?
One small but sometimes helpful difference between gerunds and infinitives is that the latter can often be used to indicate intent or purpose (a la “in order to”). That’s all Iv’e got here–the others have done a good job answering this.
Thanks guys, really helpful.