The French prefix in- and its variants il-, im-, and ir- are added to adjectives, adverbs, and nouns to create antonyms. The English equivalents are un- and in-.
Liaisons between syntactically related words, such as an article and its noun, or a subject pronoun and its verb, are required, though of course there are always exceptions.
Two dozen French verbs always require a reflexive pronoun but aren't necessarily reflexive or reciprocal. These "essentially pronominal" verbs can only be used pronominally, as without the pronoun, the verb is meaningless.