Basics
Consider these two sentences:
(A) I ride a bicycle.
(B) I can ride a bicycle.
When we add can, it appears that ride does not change. By the same method,
many learners of English make this error:
(C) He rides a bicycle.
(D) **He can rides a bicycle.
Sentence (D) is wrong. The words ride in sentence (A) and rides in sentence (C) are the
simple non-past
of the verb ride. The word ride in sentence (B) is the
infinitive
of the verb ride. Sentence (D) should also use the infinitive: its correct form would be:
He can ride a bicycle.
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