What verb form should you use after "consider" and "imagine"? Infinitive or gerund?

Consider can be followed either by a noun or a gerund (the "-ing" form of a verb used as a noun).
- They will consider the suggestions.
- I considered working.
- She considers going to the dentist.
Imagine can be followed by a noun, gerund, or that-clause.
- I can't imagine a larger dog than a mastiff.
- I can't imagine working harder.
- I can't imagine that she's telling the truth.
In both cases, when a verb directly follows consider or imagine, you should use the gerund form, not the infinitive:
- You should consider writing to him more often.
- It's easy to imagine winning the lottery, which is why I keep playing it.
A gerund is the -ing form of a verb that acts as a noun. When certain verbs are followed by other verbs, the second verb needs to be in gerund form. Consider and imagine are two verbs that must be followed by a gerund if the second word is a verb.
Consider
Consider can be followed by a noun, a that-clause, or a gerund. Here are some examples.
Followed by a noun
- Please consider the facts.
- I have considered your offer.
Followed by a that-clause
- I wish my boss would consider that I have children when he makes the schedule.
- You should consider that she might not feel the same way about you.
Followed by a gerund
- Have you considered taking a painting class?
- I will consider going back to work when my kids are in school.
Consider cannot be followed by any other form of verb besides a gerund.
- Incorrect: He considered to change his major to biology.
- Correct: He considered changing his major to biology.
Imagine
Imagine functions like consider. It must be followed by a noun, that-clause, or gerund. It cannot be followed by any other verb form.
Followed by a noun
- Imagine a world with no internet.
- I like to imagine a future where I’m rich.
Followed by a that-clause
- She imagined that she was a princess.
- Let’s take a minute and imagine that you get the part.
Followed by a gerund
- Sometimes I imagine winning the lottery.
- He imagined running his own business since he was a boy.