For some reason, many people from diverse backgrounds are interested in human language, perhaps because it is one of our species' defining traits. As my training is in linguistics, I thought I'd start an occasional series that presents an impressionistic sketch of some narrow topic in linguistics that illuminates part of the big picture of the human language faculty and mind. Thus, the goal will always be modest rather than exhaustive. The only popular renderings of modern linguistics with any appreciable readership are those of Steven Pinker: The Language Instinct and Words and Rules. I've read both, so I'll make sure to instruct via examples not covered therein, while still attempting to delight as he does. To inaugurate the series, I've chosen a topic from semantics, a subfield of linguistics barely covered in popular renderings -- for example, TLI is an overview of linguistics yet contains no proper chapter on semantics and only fleetingly referes to it elsewhere. But first, here is the rough geography of the major subfields within linguistics, just so you know which one deals with what primary concerns before I discuss particular topics from them (there is overlap of course). I've cited the accompanying chapter in TLI for reference (since many own it).
Syntax is the study of how words combine into phrases, and phrases into sentences -- those tree diagrams that analyze how the parts of "John walks the dog" combine. TLI chapter "How Language Works." Investigates a question like: when you negate something, e.g. with "not" or "doesn't," where does this negative thingy go, no matter what the sentence?
Semantics is the study of how the meaning of the individual words and their combination gives you the meaning of the entire grouping of words. No TLI chapter. Investigates questions like: how does the meaning of the word "black" and the meaning of the word "dog", plus their grouping together in the larger unit "black dog," tell us what "black dog" means.
Morphology is the study of how smaller bits of words like roots and suffixes combine together to form entire words. TLI chapter "Words, Words, Words," as well as much of WR. Investigates questions like: why isn't it OK to call a "ville" where many "losers" hang out a "losersville," and why is the correct form "loserville," even though more than one "loser" hangs out there?
Phonology is the study of sound structure -- not how you produce sound with your tongue and lungs or perceive it with your ears (which is phonetics), but what sound combinations are allowed in a language; or how individual sounds like /s/ or /t/ combine into syllables, and syllables into words, for example. TLI chapter "The Sounds of Silence." Investigates questions like: why is "brick" an actual English word, and "blick" a possible English word, while "bnick" is an impossible English word?
These are the basic four food groups of linguistics. Awhile ago Julius Moravcsik pointed out that these resemble the "constitutive factor" -- or "what stuff it's made of" factor -- in Aristotle's group of causes, or aitia (hat-tip to Razib for the aitia link). For now, I'm leaving out subfields that approach language from a different angle -- e.g., historical linguistics looks at how changes in the above take place over time; processing looks at how we string together speech or parse someone else's speech in real time; acquisition looks at how the entire language faculty develops during childhood; and evolutionary linguistics asks how and why language evolved in humans. Linguistic superstars Noam Chomsky and Steven Pinker pointed out that these latter resemble Nikolas Tinbergen's four why's of animal behavior, as well as Ernst Mayr's distinction between proximate and ultimate causes.