The subject of to infinitive

Question

I created the following sentences.

1. During this process, a lid covers the opening of the container to prevent entry of water into the container.
2. During this process, the opening of the container is covered with a lid to prevent entry of water into the container.

I know those like the second sentence are widely used, but I am unsure that the second sentence is grammatically correct because the subject (the opening) of the sentence does not agree with the subject (a lid) of the to infinitive.

The to infinitive in the second sentence may be considered as an adjective to modify a noun "a lid", but I think such an interpretation makes the sentence strange.

Answer 1

Neither instance of to prevent has a subject. This is a case of a non-finite verb clause acting as an adverbial of purpose - you are saying what the purpose of the lid covering the opening is. This, it applies to the whole principal verb clause regardless of word order, or being in the active or passive voice.

Non-finite verbs don't usually have a subject. This can be a little confusing, because the verb forms that are used in non-finite verb clauses sometimes look just like finite verbs, because English has rather a paucity of actual different forms of verbs.

In both cases, "to prevent entry of water into the container" is an adverbial of purpose applied to "the opening of the contained is covered with a lid". In the same manner, "during this process" is an adverbial of time.