I am a great fan of dictionaries. In my idiotic opinion, they are among the most underrated works of the human spirit, and should be up there with the late quartets of Beethoven, the plays of Shakespeare's final years, and Greene King Abbot Ale. The Oxford English Dictionary is the greatest of these great works, though bloody inconvenient if you just want to know how to spell "ceiling."
Dictionaries do have two side effects, however, about which I have mixed feelings. On the one hand, they encourage that humbling sense that one knows so little (and that much of that little is incorrect), and on the other that disabling sense that authority is fixed, "out there", and irreproachable.
On dictionaries, as on most things in life, there is a progressive and a conservative view. The progressive view might be summarised as "Language is an evolving, social practice between human beings, therefore current usage will always determine current meaning"; the conservative view as "Look it up and learn, you ignorant peasant." Both views are necessary, I think.
A classic example is the word "gay". When, somewhere around the year 1380, Sir Gawain is pestered in bed by a "gay lady", we need not find this any more confusing than he did, though it may make us smile more. The history of the word "gay" is described, with examples, in the Oxford English Dictionary, and fascinating it is, too. I'd never have guessed that gay people were being unambiguously referred to as, um, "gay" in print as early as the 1940s. Or, even more surprising, that the use of "gay" as meaning "lame" (i.e. "foolish, stupid, socially inappropriate or disapproved of" rather than "crippled through injury to, or defect in, a limb") dates back to the 1970s. So, both conservatives who claim a "perfectly decent word" was hijacked by queers in the 1980s and progressives who wince at the insensitivity of using of "gay" as a modish pejorative are just SO WRONG (as my daughter would say). I say "Look it up and learn, you ignorant peasants, and see quite how much language is an evolving, social practice between human beings ... etc."
But to my point: I have a good test of the extent to which a person's command of language is based on ignorance (or "usage" if you prefer). Here it is:
You will, no doubt, often have read that someone's face or body is disfigured by a "livid scar". My question to you is: What colour is that scar?
Now go and look it up in a dictionary, and I reckon 90% of you will thereafter walk more humbly before our great, but much misused, language. I know I did.