The Verb "could"
The Structure of the Verb Tense "Could".
When using as a modal verb or an auxiliary verb tense the verb "could" stays in its base form.
Could does not change form according to the subject.
Could is followed by a main verb. The main verb tense also stays in its base form. The main verb tense doesn't change form according to the subject.
|--||Subject||Could||-||Main Verb Tense||-||Positive Sentences||I||could||-||go||to the store|
|Negative Sentences||We||could||not||go||to the store|
|Questions**||Could||they||-||go||to the store|
* The 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.