Susanne Langer differentiates SYMBOLS (word-like units) from mere SIGNS (also called INDICES by Terrence Deacon and C. S. Peirce). This page is an attempt to sharpen the difference between these two.
A `sign' is defined by some sensory feature, A, (something directly available) that correlates with and thus `points to' B, (something of interest). All animals exploit various kinds of signs in their interaction with the world. The more intelligent animals are better at learning and exploiting more sophisticated signs (thus a cat will use and learn many more signs than a frog, a fish or an ant).
Note that all of these above depend on a certain statistical regularity of part A (the signal part) and part B (the behaviorally relevant part). The exploitation of this regularity requires first, detecting property A (which is not necessarily simple) and either learning or innately knowing its correlation with the B. In that case the animal can use A as a sign of B.
But some signs can be artificial and manmade (rather than natural or innate to particular species):
Words as Symbols.
One place to begin is to ask `So isn't a word like KITTY just another kind of sign?' In support, you might note that a small child would be likely to say KITTY in the presence of a cat. Since the sounds [kIDi] correlate with the presence of cat (so A predicts B), doesn't that show that this is just a sign like those above? This may be so, but a word in any language is vastly more sophisticated. Notice that:
In short, a symbol such as a word in a human language is easily removable from its context. Indeed we easily learn many words for things we have never experienced. Children who grow up in the tropics learn to correctly use words like SNOW and ICE without ever seeing snow or ice! No problem. They have heard descriptions of them in terms of words they do know, like COLD, WHITE, CLEAR, HARD, SOFT, FLUFFY, WATER, FALLING, SLIPPERY, etc. From these descriptions, they get at least some idea what these things are like - enough to read and produce the words appropriately.
This is the enormous power of human words: When you have learned a good sized vocabulary, you can use it to bootstrap to many other concepts and words. Given the possibility of cultural transmission from generation to generation, knowledge and understanding become cumulative at a very rapid rate (relative to the creation and transmission of innate knowledge).
IMPORTANT CLAIM: Apparently no living nonhuman animals are able to use word-like symbols that have properties resembling those above. There are, however, some (disputed) claims that a few individual animals (mostly higher primates like monkeys, chimpanzees and gorillas) have been trained by humans to use a small (< 50) inventory of symbol-like units using hand signs or small physical tokens.
Words (especially nouns, verbs and adjectives) seem to be the architypal symbols. But the most common use of the term symbol in everyday language is for nonwords: a flag or totem animal as the symbol of a country (bald eagle for USA, bear for Russia, etc), a cross for Christianity, star of David for Judaism, swastika for Nazism, etc.
It seems like a similar set of associations to other words can be made for such symbols. Thus, the US FLAG (I mean the graphic pattern in red, white and blue, not the English word FLAG) gets its meaning partly from its association to words and concepts like: HOMELAND, WASHINGTON, BALD EAGLE, PATRIOTISM, MOM, DAD, APPLE PIE, PRIDE, HEROISM, DEMOCRACY, `OH SAY CAN YOU SEE...', `I PLEDGE ALLEGIANCE...', SACRIFICE, etc etc.