Required to repeat 'that' and particle?

Question

I would like to know if the following short sentence is valid (correct English, I'm not asking for stylistic advice):

She proposes that novelty does not arise through external forces but is the result of a speculative tendency at the heart of computing.

Or if one must be verbose:

She proposes that novelty does not arise through external forces but that it is the result of a speculative tendency at the heart of computing.

I don't really like the duplication of 'that', so I am wondering if the first version is allowed.

Answer 1

Yes, it is:

"She proposes that novelty [does not arise through external forces] but [is the result of a speculative tendency at the heart of computing]".

The verb phrases in brackets are coordinated predicates of the noun 'novelty'.

So it is perfectly grammatical.

Answer 2

You can keep the first sentence, just add a comma after forces and tendency. You could go without the comma after forces, but because of the "at the heart of computing" phrase (which sounds like an afterthought), it comes out better to slow the sentence down in both areas, and gives the sentence more impact.