(13a) George seems quite relieved.
(13b) It's obvious George seems quite relieved.
(13c) George seems quite relieved, but his brother remains uneasy.
In each example, George seems quite relieved is a clause. But only in (13a) is the clause equivalent to the sentence. In (13b), the clause is embedded into a larger sentence. It is known as a subordinate clause. In example (13c), the clause is linked by coordination to another clause, but neither one is contained inside the other. In the next few chapters, we will be dealing with simple, one-clause sentences like (13a), but it's important to keep in mind that real sentences frequently contain more than one clause. We will return to multi-clause sentences after developing an understanding of basic clauses.
Another understanding of the sentence commonly found in traditional grammars defines a sentence to be a group of words that expresses a complete thought. Like the notional definitions of parts of speech, though, this leaves much to be desired. How can (13a) count as a complete thought while the identical string of words in (13b) and (13c) do not? How do we tell what counts as a complete thought? The more we think about it, the emptier this definition appears.
(14a) The founding of the college by Leland Stanford.
(14b) Leland Stanford founded the college.
Most people would have no problem saying that (14b) is a sentence while (14a) is not, but do they not contain all the same information? And why do we even think that (14a) is complete? If this sentence appeared in a larger essay, would it not be reasonable to claim that the whole essay expresses the writer's complete thought, and that this sentence is just a fragment of that thought? The traditional definition relies on a preexisting intuition of what constitutes a sentence. In other words, it takes for granted that we understand what it means to be complete without ever actually defining completeness.
For the moment, we will define the sentence negatively and say that it consists of at least one clause that is not contained in a larger grammatical unit. That is, if we look at texts that contain multiple sentences, the only relationship among sentences is one of simple sequence, as sentences are placed one after another. Note that there are additional restrictions on what is and is not a sentence, but they will be easier to define after we have studied more types of phrases and clauses.
 We are not considering here the "orthographic" sentence—that is a string of words that begins with a capital letter and ends with a period, question mark, or exclamation point. While this often, especially in formal writing, aligns with syntactic sentences, the two do not necessarily coincide.