Main Points
- An S on the end of a verb doesn't make it plural like it does for nouns
- We use the term "plural verbs", but verbs aren't plural themselves. Rather, they are changed based on whether or not the noun they are paired with is plural.
Clearing the Confusion
they run (why not runs?)
Why didn't we use plural form of verb "runs" since the subject is plural?
I think you are getting confused by the s on the end of the verbs. S is only used to make nouns plural. The s on the end of some verbs is coincidental.
We use the term "plural verbs", but verbs aren't plural themselves. Rather, they are changed based on whether or not the noun they are paired with is plural.
More Information
Verbs are "conjugated" when we used them. That means we take the basic "infinitive" form of a verb and change it slightly to suit two (main) things.
We change its tense - when the action took place and we change it depending on who/what the action applies to. The "who/what" takes in to account whether or not the speaker is included and how many people or things are being spoken about.
For most verbs, there is a pattern you can apply. Some verbs are irregular and you just have to learn them. I've given examples for a few verbs for two tenses below:
Present Simple Tense
This action takes place in the present or we are describing something that happens regularly.
Who/What Verb (Run) Verb (eat) Verb (be - irregular)
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Singular
1st Person I run eat am
2nd Person You run eat are
3rd Person He/She/It runs eats is
Plural
1st Person We run eat are
2st Person ------(Always the same as 2nd Person Singular)-------
3rd Person They run eat are
Just adding an s (or sometimes es) to 3rd person plural is the pattern for a lot of verbs.
Simple Past Tense
This action took place in the past. It has already finished.
Who/What Verb (Run) Verb (eat) Verb (be - irregular)
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Singular
1st Person I ran ate was
2nd Person You ran ate were
3rd Person He/She/It ran ate was
Plural
1st Person We ran ate were
2st Person ------(Always the same as 2nd Person Singular)-------
3rd Person They ran ate were
A lot of verbs just add -ed, for past tense but a lot don't!
I can't think of a common pattern for learning the past form of a verb, but the regular verbs tend to use the same work for all people.
Some examples:
Infinitive = Past
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run = ran
eat = ate
drink = drank
read (pronounced "reed") = read (pronounced "red")
write = wrote
kneel = knelt
see = saw
tell = told
Some that do use -ed
need = needed
walk = walked
spell = spelled (but also spelt)