English Verb Tense & The Use of "Could"

How is the verb tense "could" used?

The English verb "could" is used as both an auxiliary verb and a modal verb? Could is almost always used with a main verb tenes.

• Could is used as the past tense of "can".
• Could is used to is used to request something in the present tense.
• Usually when could is used in the present tense, it is used to ask a question.

Examples:

• Could the girls come with me to the store?
• I could not go to the moves last night, I had to study.
• We couldn't help you clean the house.

Structure of "could":

1. When using as a model verb or an auxiliary verb the verb "could" stays in its base form.
2. Could doesn't change form according to the subject.
3. Could is followed by a main verb. The main verb also stays in its base form. (The main verb that is used with could doesn't change form according to the subject.)

* All subjects are: I, we, they, you, plural nouns, singular nouns and uncountable nouns.

**Questions - When could is used to ask a question, could comes before the subject.

English The Easy Way : English Grammar : Various Verb Tenses