By the side of konter- international usage necessitates a certain number of words with the Greek ANTI-: antimilitariste, antialkoholisme, antisemito (-ido), etc., chiefly in technical and learned words.
The most general negative prefix is NON-, which is simply the adverb for 'not' preposed: nonexistant, nonposibli impossible, nonreal unreal, nonvidabli invisible, nonsavo ignorance, etc.
It would create unnecessary difficulties if instead of this perfectly clear and unmistakable prefix non- we were to take the L in-, which in so many words is used in a totally different meaning (from the preposition in). Occ commits this mistake, but it necessitates the rule that this in is to be provided with an accent, and the express warning that it must not be confounded with the other (unstressed) in, thus ínscrit = N nonskriptet, inscrít = enskriptet; inhabitabil with different accent means habitable and uninhabitable. If in- is taken as a negative prefix, we may just as well have it in the four forms found in national languages, in-, im-, il-, and ir-; but that would be both impossible, immoral, and irrational in a rational international language.
DES- is different from non through denoting the direct opposite: nonutili is not-useful, i.e. useless, desutili would be hurtful; desagreabli, desavantaje, desorganisa, desaproba, descharja discharge, desobedia disobey, desfasil difficult, desquieti anxious, etc.
DIS- implies a totally different notion, though the two have found the same form in E: it means dispersion or separation: disdona distribute, give promiscuously to several people, dissenda send in different directions, distrancha carve. (Instead of dis-solu we say disolu.)
MIS- (E D Sc, F mé-) is used with verbs to denote 'wrongly': mispronuntia, miskomrenda misunderstand, misdukte lead astray, miskalkula, etc.
MAL- as a prefix corresponds both to the adjective mal(i) bad and the adverb malim badly: malodoro stink, maledukat ill-bred, malformat ill-shaped, malhumorosi ill-tempered, malfamosi ill-famed, etc.
PAR- denotes perfect or thorough action: parlerna learn perfectly, parlekte read thoroughly, read to the very end, while tralekte means simply read through, which may be done cursorily.
RI- implies repetition or restoration; while the original meaning of L re- is often lost in words beginning with re-, this ri- is used where E has the full long vowel (as in re-cover, re-form distinct from recover, reform): rielekte re-elect, ridona give again, riskripte write again, etc. Ri may be used also as a separate adverb: me have ri li plesire I have again the pleasure.
RETRO- back(wards), inverse action: retrotira retire, retroseda cede back, restore, retrodukte lead back; li lege non have retroaktiv efekto.
MI- corresponds to duimi(m) half: mihore half-hour, milume twilight, miklosat half-closed.
BO- indicates relation by marriage: bopatro father-in-law, bofilia, etc. Different from stif- = E step: stifmatra, etc.
EX- is used as in most European languages for 'late, former, retired': exrego, exprofesoro.
ARKI- corresponds to E arch-: arkiepiskopo archbishop, arkianjele archanjele archangel, arki-diakono, -duko.
PSEUDO- is taken from Greek like the preceding, and like it used in many living languages: pseudoprojeto, pseudofilosofo, pseudosientiali, etc.