In grammar, clause structure refers to the classification of sentences based on the number and kind of clauses in their syntactic structure. Such division is an element of traditional grammar. A simple sentence consists of only one clause. A compound sentence consists of two or more independent clauses. A complex sentence has at least one independent clause plus at least one dependent clause. A set of words with no independent clause may be an incomplete sentence, also called a sentence fragment. A sentence consisting of one or more dependent clauses plus two or more independent clauses may be called a complex-compound sentence or compound-complex sentence. Sentence 1 is an example of a simple sentence. Sentence 2 is complex, because “so” is considered a subordinating conjunction in English, and sentence 3 is complex. Sentence 4 is compound-complex (also known as complex-compound). Example 5 is a sentence fragment. I like pumpkin pie. I don’t know how to bake, so I buy my sweets. I enjoyed the apple pie that you bought for me. The dog lived in the garden, but the cat, who was smarter, lived inside the house. What a silly dog. The simple sentence in example 1 contains one clause. Example two has two clauses (I don’t know how to bake and I buy my sweets), combined into a single sentence with the coordinating conjunction so. In example 3, I enjoyed the apple pie is an independent clause, and that you bought for me is a dependent clause; the sentence is thus complex. In sentence 4, The dog lived in the garden and the cat lived inside the house are both independent clauses; who was smarter is a dependent clause. Example 5 features a noun phrase but no verb. It is not a grammatically complete clause.