What characterizes human beings most clearly as being different from all other animate beings is their ability to use language as a tool for cooperative (and sometimes not so cooperative) communication of their ideas, for conceiving and handing down complex systems of knowledge, and for changing these systems, if felt to be necessary. In addition, human beings use language to express their feelings, to make each other feel comfortable -- or uncomfortable, to talk about God -- and the world, to compose poetry, and even to talk about language. Language is therefore central to our being human and, as such, represents perhaps the most worthy subject for intellectual investigation.
Most people take language for granted in ordinary life. This is not surprising since speaking and understanding language proceed without our being aware of how much mental or physical activity is involved. To understand even a simple sentence like "The cat is on the mat," for example, we have to recognize the sequence of sounds as a sequence of words belonging to a language we know, recognize how the words go together in successively larger groups, and recognize how the meanings of the constituent parts combine to determine the meaning of each group. Yet little children learn how to do this without even knowing that they are doing so and without serious formal instruction. When the same children become adults, they find acquiring a new language quite difficult, especially without explicit analysis or formal instruction.
Linguists generally are agreed that the reason children learn their first language so effectively and without any conscious effort is that human beings are genetically programmed somehow to learn language. Moreover, children acquire language in "chunks", suggesting that what they learn is general principles, not expression-specific rules. In fact, some linguistics believe that the very nature of these principles is in its broad outlines predetermined by our genetic endowment.
These are the types of puzzles that engage linguists. But since knowledge of language is below the level of consciousness, it requires special techniques to bring it to the level of consciousness and to investigate such puzzles.
The two fundamental aspects of linguistic structure that are studied by linguists are PHONOLOGY (the sound structure of language), and SYNTAX (the manner in which we combine words into sentences). But many other aspects of language likewise attract the interest of linguists. These include MORPHOLOGY (word-formation and inflections), SEMANTICS (how words and sentences "mean"), PHONETICS (how we produce and recognize speech sounds), SOCIOLINGUISTICS (how language is used in society, and how social factors determine the nature of language use), PSYCHOLINGUISTICS (which, among other things, studies linguistic behavior and psychological processes underlying that behavior), and COMPUTATIONAL LINGUISTICS (dealing with the "interface" between computer science and linguistics). Finally, like all other aspects of human life, languages have histories. Thus, present-day English differs so much from the Middle English of Chaucer that we might as well call them different languages. Issues connected with language as an historical phenomenon are addressed under the heading HISTORICAL and COMPARATIVE LINGUISTICS.
In all of these activities, linguists (like other scientists) look for the most general explanation of the facts they are concerrned with. Rather than studying individual words or phrases, linguists have to abstract away from the details that obscure these generalizations. Linguistics, therefore, tends to be a field that requires a fair amount of abstract reasoning and is, in this respect, similar to the natural sciences.
Besides being intellectually stimulating and satisfying in its own right, the study of linguistics also has some practical advantages: Training in linguistics can be extremely useful as preparation for foreign language teaching as well as for the very lucrative field of Teaching English as a Foreign Language. It also provides a good foundation for study in fields such as Anthropology, Speech and Hearing Science, Psychology, Cognitive Science, Artificial Intelligence, Computer Science, Lexicography, Stylistics, Text and Discourse Analysis. Combined with a good language background, it also is useful for those interested in "Area Studies", such as Asian and African Studies. Finally, of course, an undergraduate degree in Linguistics provides a solid foundation for further linguistic study at the graduate level.