One thing I didn't appreciate about English until reading a Europe forum for a while is that it has a lot of different prefixes that mean something like "not", and this is not very intuitive to people learning the language. Their use is not regular.

Consider:

• "a-" as in "atypical"

• "non-" as in "nonconsentual"

• "un-" as in "uncooperative"

• "im-" as in "immortal"

• "in-" as in "inconsiderate"

• "il-" as in "illegitimate"

• "mal-" as in "maladjusted"

• "anti-" as in "anti-establishment"

• "de-" as in "deconstruct"

And sometimes, some of the prefixes are associated with base words to form real words with similar meanings, but meanings that are not the same. For example, "immoral" and "amoral" do not mean the same thing, though they have related meanings.