Does the parallel structure break when we use pronouns?

Question

First of all, I know that this sentence obviously preserves the parallel structure:

The experiment on wild animals yields results not only to understand their eating habits better but also to encourage future studies.

But, does it still maintain the parallel structure if I modify the sentence using pronouns to express the first phrase:

The experiment on wild animals yields results to understand their eating habits better, not only that but also to encourage future studies.

Or, even this - using gerund instead of the verb in the last phrase:

The experiment on wild animals yields results to understand their eating habits better, not only that but also encouraging future studies.

So, which of these examples do not violate the parallel structure? I am really confused by this topic. Also, when I put the second sentence to Grammarly, it give me a recommendation to delete pronoun that.

Answer 1

Whatever “the parallel structure” is — something known to people learning English but not to the average native speaker, perhaps — as a scientist I would say that the starting sentence is poor, even if grammatically correct.

The problem for me is:

…results to understand

The infinitive after the noun makes no sense without indicating who is understanding. If the infinitive is preserved write:

…results that (not only) allow one/us to understand

Alternatively, albeit making an abstract noun from a verb (something I discourage):

…results that (not only) allow understanding of

So in the second part of the sentence the infinitive is removed and becomes:

(results) …but (that) also encourage further studies

…in both my suggestions.

As to the two variants:

“Not only that” is something of an oratory device. If you use it you are best advised to start a new sentence and repeat “results”.

If you want to use the gerund, this will modify results, but you can’t use it in the same sentence if you have already used the different relative construction after “results”. Again, start a new sentence and repeat “results”.

In addition “their” is too far from the noun it qualifies. Not much one can do about this without repeating “animals” but the moral is that if a sentence doesn’t feel right, one should look carefully for the reason and not assume that is the first thing that comes to mind. Most often the solution is to divide it into two.

Answer 2

The first two are parallel and under the scope of your intended expression, and are just the same, as long as the reader is agreeing or honest and his receive.

The third gets out of the cycle when you say encouraging. Why, because it covers the whole sentence, to keep it bound like the first two, you can use "encourages".

As a matter of taste, I would definitely choose the first, because it's more reasonable to mention the findings and then express the extras.