Unfortunately, I can't remember where I've read the following rule, but it went something like: Don't use "like" in place of "as". "Like" governs pronouns and nouns. "As" governs phrases and clauses. Is this true? If so, does that mean the below is wrong: His head was as strong as a hammer. And instead, it should be: His head was strong like a hammer. Because "hammer" is a noun and not a phrase or clause? I could use some clarification on this. Thanks very much.