I recently had a nice email discussion with a well-established, Hugo- and Nebula-Award winning novelist and short story writer. I complimented him on the readability of his prose. And he told me that one of his secrets is that he never uses a Thesaurus or the Thesaurus function on his word processor. His opinion is that if you have to stop to find a word, the reader will have to stop to understand the word. And the one thing he doesn't want to do is write prose that forces his readers to stop writing.
Robert Masello most definitely agrees with him. In his third rule, Masello advocates using the words that come most naturally to you when you write.
And I agree as well.
Some writers out there are beautiful stylists, crafting prose that dazzles the eye and delights the ear. And as much as I would like to count myself among their number, I know that I cannot. My style tends towards the plain, the ordinary, the unornamented -- and that is the only way I know how to write.
Furthermore, some stylists break through the barrier of beautiful prose and fall into the trap of extreme prose. I've picked up many a book or story, tried to read it, and felt turned away by the writer's attempts to present the most gorgeous, overrated prose -- at the expense of simply telling the story. If the words a writer chooses don't work towards that goal, they have no business being there. And if you feel the urge to go for the thesaurus, you should probably ignore it.
Of course, I will admit that there are exceptions to this rule. If you're trying to write a pretentious character who prides himself on his advanced vocabulary -- say, perhaps, a Harvard graduate -- then, absolutely, equip him with the most obfuscating verbiage you can. And let us not forget Mark Twain's dictum: The difference between the right word and the wrong word is the difference between lightning and the lightning bug. If you truly know that the best word for the job is one you need a thesaurus for, then perhaps it's okay to do so, just that once. But in general, we ought to curb our sesquipedalian natures, eschew obfuscation, and strive for clarity.