A correctly worded subject and predicate can form a dependent clause that, by itself, cannot function as a sentence. Adding a subordinate conjunction to the beginning of a clause will change it from an independent to a dependent clause. The clause "I like sports" is a complete sentence, but "Though I like sports" is not. However, if you were to replace the conjunction with a sentence adverb or adverbial phrase, such as "frankly," "on the other hand," or "however," it would be an independent clause and a complete sentence. Another common error is using a noun phrase which is modified by a dependent relative clause as a sentence. Consider the incomplete sentences "His opinion that she likes sports" and "The fact he likes sports." Both of these phrases can easily by made into sentences by adding the word "is." Consider "His opinion is that she likes sports" and "The fact he likes sports is important." We combine clauses in complex sentences more often when we write than when we speak. Writing well requires practice, and we often need to revise our first drafts.