The case of “aloud” and “allowed” is a perfect example of the problem caused by people being taught only to pronounce words, not understand them, and of them thinking written words are merely transcriptions of sounds rather than having inherent meanings. Both words (at least in the primary dialects of English) are pronounced the same. Their meanings, on the other hand, are totally different. If you’re only trying to figure out how to write down the sound /ʌˈlaʊd/ the odds are 50/50 you’ll get it wrong. But if you know what the words mean, not a chance.
So let’s look at those two words: aloud and allowed.
Right away, we can see something important there: allowed looks like a form of allow. So if the intended meaning is permitted, such as whether or not PvP is permitted on a server, or perhaps building underground bases, sky bases, and so on, we know that’s our word. If someone asks “Do you allow PvP?” the answer would be “PvP is allowed,” right? So we’ve got a good handle on what allowed means.
But what about aloud? That’s a bit weirder. It sure looks like it’s related to sound — there’s that -loud in there. And, of course, it is. But there’s also that leading a-, and those can be weird. Sometimes it means “not,” sometimes it means “on,” sometimes it’s a way of changing parts of speech, like living to alive. A lot of words, from several of the languages that contributed to English, were worn down to that stub of an a- and, more often than not, you have to just stare at the thing for a while and hope a meaning falls out.
That’s the case with aloud. We can be fairly sure we’re not dealing with the meaning of a- that means “not” because aloud certainly doesn’t mean “quietly.” Anything but, actually. We know if we’re reading aloud, we’re not sitting silently in a corner with our newspaper (or ebook reader); we’re saying something. Loudly. Wait, now we’ve got something: Loud is an adjective — a word that describes a noun. When you hear a loud voice it’s definitely louder than a quiet voice. And aloud is an adverb — a word that describes a verb. You can read silently, or you can read aloud. Clearly silently and aloud are the same part of speech, since they’re interchangeable there, and silently has that telltale -ly that marks so many adverbs. So aloud must be an adverb, and the a- is a prefix that changes the adjective loud into the adverb aloud.
Most of that last paragraph, though, is unnecessary if you’re just trying to figure out which one to use in a sentence. You know you want /ʌˈlaʊd/ in some form. If the sentence is about allowing something, you need allowed. It’s obvious, right? And if it’s about sound, instead, and whether or not that sound should be loud enough to hear, you need aloud. Once you spot the allow and loud in those words it’s clear which is which.
Written words aren’t just ways of indicating sounds. They have their own inherent meanings. When you look at them closely, you can see what those meanings are. And you’re allowed to brag aloud that you know this now.