Why is the word "pervious" uncommon to the point of being considered a spelling error, but "impervious" is extremely common?
For the record, it is a word, apparently. Dictionary.com defines it as:
- admitting of passage or entrance; permeable: pervious soil.
- open or accessible to reason, feeling, argument, etc.
My general sense is that these kinds of opposites (formed with in-, im-, etc.) tend to be either well balanced in usage, or the "positive" form is more common. Consider:
- perfect / imperfect
- possible / impossible
- plausible / implausible
Google NGrams support this perception:
There are a few exceptions to this rule of thumb. "Insurmountable" seems more common than "surmountable," for example. This is again reinforced with an NGram:
The word "pervious" seems so odd that at first I thought that the word "impervious" must have derived from some completely different source and the presence of im- was just a coincidence. But, no, the etymology clearly points to a root where the positive form "pervious" (from the Latin "pervius") is (was?) valid.
I've considered that the word is just too similar to the abbreviated form of "pervert," which obviously has a strong negative connotation. But this doesn't appear to be a well-reasoned or satisfying answer. Lots of perfectly valid words are superficially similar to words with negative connotations. (Think of a "niggling" pain, for example, although admittedly this example is more common in British English and the racial slur it's similar to is likely more common in American English.) Bottom line, I doubt that people aren't using "pervious" because it's similar to other words.
So this leaves me wondering:
- What happened to the word "pervious"? Why is it so much less common than "impervious"?
- Is there a known class of such words where the opposite (formed by a prefix) of a word is dramatically more common than its base?
Any thoughts would be much appreciated!