Apparently I have a real spelling blindspot. Now, I've noticed before that there are some words which I consistently misspell, but generally they could conceivably be spelled that way without much change in pronunciation.

It seems to be getting worse. Latest thing is the word substitution. I think it's the repetetetitive nature of the middle of the word, but I had spelled it correctly in one out of seven or eight occurences in one document. And in each of these places, it was extremely difficult to tell whether the spelling was right or wrong; I was reduced to slowly sounding out the word, syllable by syllable.

Substition may indicate a little forgetfulness. I'm not quite sure what one should take from substitionion.