Moods and modals

If in other languages (hixkaryana) moods and modals are both expressed with clitics, is there a formal difference? Is mood a system akin to speech acts, while modals express attitudes toward the statement rather than a transaction with the hearer? Is the difference purely semantic with no formal difference? If so, what kind of transaction is the subjunctive? "Si hubiera sido..." "If I had been..." simply attaches to a declaritive?