A quick writing question

<p>For this sentence:
"To keep your engine running in the freezing cold is a good way to keep the car’s interior warm and cozy."
How do you know if you have to change the gerund to an infinitive or the other way around? It seems kinda obvious for this one but some times I can't tell if I should use gerund/infinitive when both are present.
Thanks!</p>

<p>Whenever you are unsure It is probably wise to just substitute the gerund for the infinitive
and normally it is clear which one sounds better. I have not come across a question that
doesnt ‘sound wrong’. Sometimes you will need to use an infinitive instead of a gerund to make something more parallel. This is where maybe you dont really know when to use the infinitive or gerund. So what I suggest is that if it is not clear whether to use the infinitive or the gerund, check for parallelism.</p>

<p>^
this was the question that I had trouble with:
"some scientists believe that mentally stimulating activities may increase the number of brain cells available to replace if any/available, replacing if any) are lost through aging. It sounds fine for both choices but the gerund > infinitive tip doesn’t work here. how would you solve this?</p>

<p>The two options, gerund versus infinitive, in your last post are unclear. There is possibly a typo in your example. Can you write out each of the two options.</p>

<p>Some scientists believe that mentally stimulating activities may increase the number of brain cells available to replace any that are lost through aging</p>

<p>vs. </p>

<p>Some scientists believe that mentally stimulating activities may increase the number of brain cells available, replacing if any are lost through aging.</p>

<p>The second form (with the gerund) is grammatically incorrect. The grammar error is unrelated to your original question of gerund vs. infinitive. The agent for “replacing” is unclear. Who does the replacing?</p>

<p>The first form (with the infinitive) is at best awkward. The reason is unrelated to your original question.</p>

<p>One way to rewrite your sentence, while avoiding both infinitive and gerund is:</p>

<p>Some scientists believe that mentally stimulating activities may increase the number of brain cells available for replacement of those lost through aging.</p>

<p>I expect that you can find reasonable usage examples where both the gerund and infinitive form are acceptable. I’ll see if I can come up with one or two.</p>