In a typical English sentence, the subject is first, and the verb is second. The subject is who or what the sentence is about, and the verb expresses an action or state of being. In the simple sentence "Mary left work," the subject is "Mary," and the verb is "left."
A simple sentence expresses a complete thought using one independent clause. Other examples of sentence structures include a compound sentence, which contains at least two independent clauses united by a semicolon or a conjunctive word. A complex sentence contains an independent clause and a subordinate clause, which does not express a complete thought. A compound-complex sentence contains two or more independent clauses joined with one or more subordinate clauses.