A sentence is a linguistic unit consisting of one or more words that are grammatically linked. A sentence can include words grouped meaningfully to express a statement, question, exclamation, request, command or suggestion. A sentence is a set of words that in principle tells a complete thought (although it may make little sense taken in isolation out of context); thus it may be a simple phrase, but it conveys enough meaning to imply a clause, even if it is not explicit. For example, "Two" as a sentence (in answer to the question "How many were there?") implies the clause "There were two". Typically a sentence contains a subject and predicate. A sentence can also be defined purely in orthographic terms, as a group of words starting with a capital letter and ending in a full stop. (However, this definition is useless for unwritten languages, or languages written in a system that does not employ both devices, or precise analogues thereof.) For instance, the opening of Charles Dickens's novel Bleak House begins with the following three sentences: