I am painting the walls to brighten up the room.

[T Shirt Carrot]

Can someone please explain why 'to' is a preposition rather than a conjunction when there are many sentences where 'to' appears to be a conjunction.
Examples:

I am painting the walls to brighten up the room.

There's never been a better time to clean my car.

 

[5jj]

To is neither a preposition nor a conjunction in those sentences. It is best thought of as part of the full infinitive.

 

[jutfrank]

The word to in those sentences is not a preposition but an infinitive marker. That means that the verb following it is in the unmarked base form.

[cross-posted]

 

[5jj]

there are many sentences where 'to' appears to be a conjunction.

To is never a conjunction.

 

[Rover_KE]

Welcome to the forum, T Shirt Carrot. ;-)

What makes you think 'to' can be a preposition or conjunction in that context?