Well, when the "Area of Effect" button is "darkened" (such as it is), the spell will only hit one target - if you enable AoE casting by either typing /aoe in the chatbar or by pressing the button or key you have bound to "Emote Menu/Stack Battle Commands" (dunno what the default is on a keyboard, sorry), it'll light up and look like << Area of Effect >> to warn you that it's going to hit more than one target. While I haven't done much research on the subject, yes, AFAIK, all the spells except Spirit Dart/Phantom Dart (which aren't really spells anyways) can be either single or AoE-targeted.
FFXIV: Raji Skybrand (Leviathan)
Give a man a fish, he'll be fed for a day. Teach a man to fish, and he'll scream "F*** off noob, I know what I'm doing!" and continue to do it wrong.