A digression on spelling
One of the things that writing WanderingThoughts has been good for is giving me a good exposure to all of the spelling mistakes I make routinely. I've long been interested in linguistics, so I find spelling mistakes that happen all the time interesting, since I suspect that they're a sign of deep linguistic mechanisms at work. (Unfortunately I don't know enough linguistics to know what they are, or if anyone's ever studied the field.)
I believe that I generally spell words phonetically, but based on how they sound in my head instead of how I say them out loud. Sometimes this points to odd differences; as I noticed in writing yesterday's entry I pronounce independent correctly out loud (I think), but inside my head it seems to be independant. Only time will tell if my internal pronunciation has shifted, now that I've prodded myself about it. (I know that writing WanderingThoughts has helped with some of my common spelling mistakes.)
Consistent spelling mistakes by other people can be equally fascinating. For example, people habitually spell my last name 'Siebermann' instead of 'Siebenmann', even when they have the correct version literally in front of them. A mistake so common strongly suggests that there's an underlying linguistic mechanism in action.
Strictly speaking homonym errors are not spelling mistakes, but they're so common that there's got to be a linguistic mechanism at work. I usually get the common your versus you're and its versus it's right; the one that bedevils me is whose versus who's, to the point where I just incorrectly fixed one of my past entries and then reverted it. I can get it right if I slow down to think and expand the contraction, but my gut thinks whose just looks wrong. (A lot of what I write is based on what looks right, or sounds right inside my head; this is partly why I machine-gun commas around.)
Sidenote: typos versus spelling mistakes
My operating definition is that typos are mistakes that I do only once and that look wrong to me once I'm paying attention, whereas spelling mistakes are mistakes I do consistently and that look right to me when I scan. Teh is a typo (a letter transposition), whereas independant is a spelling mistake. (I make typos all the time; the delete key is really my friend.)
I sometimes make a third type of errors, word substitutions, where one word should go into the sentence but for some reason another will pop up instead; it's especially prone to happen if I'm thinking about two things at once. For example, in the above aside I first wrote type instead of time.
I tend to believe that anything above the level of typos is a sign of interesting internal linguistic processes.