Rules for writers, Tenth edition - Diana Hacker, Nancy Sommers 2021

Use nouns (including -ing forms) after prepositions
Prepositions and idiomatic expressions
Multilingual Writers and ESL Topics

In a prepositional phrase, use a noun (not a verb) after the preposition. Sometimes the noun will be a gerund, the -ing verb form that functions as a noun (see 49b).

Distinguish between the preposition to and the infinitive marker to. If to is a preposition, it should be followed by a noun or a gerund.

If to is an infinitive marker, it should be followed by the base form of the verb.

To test whether to is a preposition or an infinitive marker, insert a word that you know is a noun after the word to. If the noun makes sense in that position, to is a preposition. If the noun does not make sense after to, then to is an infinitive marker.

✵ Zoe is addicted to .

✵ They are planning to .

In the first sentence, a noun (such as magazines) makes sense after to, so to is a preposition and should be followed by a noun or a gerund: Zoe is addicted to magazines. Zoe is addicted to running.

In the second sentence, a noun (such as magazines) does not make sense after to, so to is an infinitive marker and must be followed by the base form of the verb: They are planning to build a new school.