[Grammar] To as infinitive marker and To as preposition

[Checkmate]

"I want to cry."

"I'm used to driving."

How do I know the difference between "to" as the infinitive marker and "to" as a preposition?

 

[MikeNewYork]

These are both infinitive markers.

 

[TheParser]

"I'm used to driving."

***** NOT A TEACHER *****

"Be used to can be followed by nouns or -ing forms (NOT infinitives)."

-- Michael Swan in Practical English Usage (1995), entry 578 on page 605.

Mr. Swan gives this example: "It was a long time before she was completely used to working with old people."

Mr. Swan reminds us that "used" in this structure is an adjective.

Therefore, I believe that we can reasonably conclude that "to" is a preposition in that sentence.