Learn Italian: Più un trattore è moderno, meno benzina consuma. - The more modern a tractor is, the less gas it consumes.

In English, correlative proportions use 'The more... the less...'. In Italian, you never use the definite article here. It is always just Più... meno.... If you added the article and said Il più, it would mean 'the most' (the superlative), which would break the structure of the sentence.

Why are Più and moderno separated by the subject and verb? In English we say 'The more modern...'.

When più or meno modifies an adjective in these structures, Italian normally puts più/meno at the start of the clause, followed by the subject, the verb, and then the adjective. So you say Più un trattore è moderno, rather than grouping them together as Più moderno un trattore è.

But in the second half, meno and benzina stay together (meno benzina). Why the difference?

Because here meno is modifying a noun (benzina) to express a quantity ('less gas'). When più or meno modify a noun directly, they must stay attached to it, so the phrase meno benzina sits together as a single block before the verb consuma.

In American English we call vehicle fuel 'gas'. Could I just say meno gas consuma?