Question 1

How can I tell which "used to" structure to use?

Accepted Answer

Ask yourself: am I talking about the past or the present? If you are describing something from the past that is no longer true, use "used to + infinitive": "I used to live in London" (past, not anymore). If you are describing what feels normal or familiar now, use "be used to + gerund": "I'm used to living here" (it feels normal now). The verb tense also helps: "used to" is past only — you cannot say "I use to smoke." "Be used to" can be any tense: "I am used to it," "I was used to it," "I'll be used to it." This tense difference is a useful check.

Question 2

Why does "be used to" take a gerund while "used to" takes an infinitive?

Accepted Answer

The structures are grammatically different despite looking similar. In "used to smoke" (past habit), "used to" functions as a single unit like a modal verb, and modal verbs take infinitives. In "be used to working" (accustomed), "to" is a preposition meaning "to something." Prepositions always take gerunds: "accustomed to working," "familiar with driving," "comfortable with travelling." You can test this: "I'm used to hard work" (noun after preposition) proves "to" is a preposition. "I used to hard work" makes no sense, proving "used to" is a different structure.

Question 3

What is the negative form of "used to"?

Accepted Answer

The negative of "used to" (past habit) is "didn't use to" or "used not to": "I didn't use to like vegetables" or "I used not to like vegetables." The second form is more formal and less common. Note: "use" loses its -d in the negative and question forms: "Did you use to smoke?" not "Did you used to smoke?" For "be used to" (accustomed), the negative follows normal verb patterns: "I'm not used to getting up early" or "I wasn't used to the climate." Questions use standard inversion: "Are you used to living here?" Cambridge exams test both negative forms.

Gerunds and Infinitives: Be Used To vs Used To

Quick Rule

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Gerunds and Infinitives Error Correction

Common Gerund and Infinitive Verbs

Preposition + Gerund

-ed vs -ing Adjectives

Conditionals

Present Perfect