Prefixes, how and where to use negative prefixes like un-,dis,non-,etc?

this stupid dictionary site thinks UNTHAW is a word

-- emphasis on stupid!

I agree that sometimes it's just best to drop it.

CJ

[pr] where the word has another [nasal] feature, <img src="/emoticons/emotion-67.gif" alt="Camera [P]" />, <img src="/emoticons/emotion-56.gif" alt="Sleep [S]" />, [v], <img src="/emoticons/emotion-65.gif" alt="Kiss [K]" />, = NON (Non-Venerial)
[VOWELS], [kw], [pr], I.e Elsewhere = DIS (Dis-Affected)

UN distinction is semantic, not phonologically driven.

Also these prefixes were most likely separate words origionally and over time changed to the bound morpheme we know them as. I see that most of them are semantically driven but there is a distiction between NON and DIS as above from the data I saw.

Google should be able to help you with suffixes.  There are many!

Here's a good list:  http://www.paulnoll.com/Books/Clear-English/English-suffixes-1.html

There are several pages of suffixes at that site.

CJ

cute

There are some rules to help you remember.  This chart always helps my students.

ir  - used before r - irrelevant, irresponsible

il - used before l - illicit, illogical, illegal

im - used before p,b,m - imperfect, impossible, immoral,

in - used before all other letters - uncomfortable, unexceptable

un, non, and dis have no rules and require a little memorization