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3a) A cat ate the small animal.

3b) A cat is a small animal.

The syntactic analyses of the two sentences are differents. In the sentence 3a) we have (s, v, do) while, in the second sentence 3b) we have (s, v (copular), sP).

In 3a) “a cat “is noun phrase (a is determiner indefinite article, cat is head noun of noun phrase “a cat”), ”ate“ is verb in past simple tense,” the small animal “ is noun phrase consist of determiner “the”, “small” is adjective , “animal” is the head noun of the noun phrase, all the noun phrase functions as direct object.

In 3b) “a cat“ is noun phrase (a is determiner indefinite article, cat is head noun of noun phrase “a cat”) function as subject, “is” copular verb in simple present tense,” a small animal” noun phrase consist of the indefinite determiner “a” , the adjective small , and the head noun of the noun phrase “animal”, the noun phrase function as subject predicative.

Differences in the meaning: the first sentence means that there was a cat and it ate the small animal "the small animal" should be mentioned before, or known to the reader, while the second sentence means that a cat is a kind of animal and it is small. We are talking generally here.

Comments  
Good analysis, Somer. Do you have a question about it?
thank you very muchEmotion: thinking