1. He knifed a person last night.

Question

2. He knives a person every year.
3. He knifes a person every year.
4. There are three knives on the table.

Which one is incorrect among the four?
Would you check the conjugation of the verb knife or the noun knife?

Answer 1

#2 is not correct; #3 is correct, as are #s 1 and 4.

VERB:
to knife (to stab with a knife)

knife = present form with knifes when the subject is 3rd person singular

knifed = simple past form

knifed = past participle form (used with "to be" and "to have" auxiliary verbs)

NOUN:
knife = singular
knives = plural
knife's = singular possessive
knifes' = plural possessive

Answer 2

Sorry. That last noun form should be knives' -- since it's plural!