Can you tell me why it's isn't grammatically wrong to put the in front of sandwiches in the sentence It was the sandwiches that he bought at the store?

Answer 1

Context is key, and we have no way of knowing that in this instance. For example, if the question was asked, "Did Ethan buy Sandwiches or potato chips at the store?", the answer might be "It was sandwiches that he bought at the store." and the "the" is superfluous. On the other hand, if the question was, "What is that mess that Ethan dropped on the sidewalk?", the answer could very well be, "It was the sandwiches that he bought at the store." Ethan may have bought a few things at the store, the definite article specifies what he dropped.