How would I explain the error the boy made and how to explain the proper form to him?

Question

The boy says “My dad did not bought me a dog last year.”  How would I explain the error the boy made and how to explain the proper form to him?

Answer 1

"Did" is the past tense and therefore does not need another past tense verb. Think of "did walk", "did swim", or "did catch." The negative does not effect the tense. "My dad did buy me a dog last year" or "My dad did not buy me a dog last year."

Answer 2

It depends how old the boy is! For purposes of the explanation, let’s go with ages 9-12. Did is always used in its base form, which is did. It’s a helping verb for the past tense. Since did is “helping” out the main verb, which in this sentence is buy or bought, it helps the main verb to be in the past tense. Therefore the main verb does not need to be marked for tense, because the helping verb took care of the that. The past tense is shown by the helping verb, or for older students, “auxiliary” verb. In a sentence about the past without an verb, the main verb does need to be in the past tense form, and the sentence would read, “My dad bought me a dog last year.”