Music is an uncountable noun in most senses: that is a word that refers to a group or an amount of something, or to some broad concept that there cannot be two of.
Music is an art or a human category of sounds; it is not a particular instance of something related to this art. For such an instance, you could use piece of music, song, number, movement, ballad, ouverture, etc., depending on what kind of instance you were thinking of.
The same applies to nouns like water: you can't say "I have two waters for you" (except in special circumstances), but rather "two gallons of water", or "two cups of water". Nor could you say "I have many loves for you", or "could you move a couple of sands closer to the beach". A few instances of common uncountable nouns:
- a piece of music
- a piece of information
- a piece of advice
- a grain/pinch of salt
- a piece of furniture
- a piece/scrap of paper
- a blade/patch of grass
- a piece/log of wood
As you see, specific kinds of instances of uncountable nouns can be indicated by different countable nouns, such as piece, grain, patch, etc. Some of these uncountable nouns can be countable if used in a different sense. Note that it is not always obvious from meaning whether a noun is countable or not: to some extent that is something that needs to be learnt word by word, alas.
Your search for a rule is admirable, but alas! doomed to failure.
- The plural of fish is fish. Unless you're differentiating between species:
The smaller fishes are more affected by ocean warming than the larger.
Or if you are a mafioso, in which case you say
Vinnie sleeps with the fishes.
Of if you're a theologian discussing the miracle of
the loaves and fishes.
Different species form plurals in unpredictable ways. Both tuna and salmon are their own plurals. Species that end in -ing, like the ling form their plurals by adding a final s, except for grayling and herring. You just have to look it up here. However, if the fish name is the name of a special at your restaurant, you might hear a waitress call out
I need two salmons and three tunas!
She means two orders of the salmon dish and three of the tuna dish.
No matter how many you have in a bowl, you only have fish, never fishes.
- Cakes is the plural of cake. It never means pieces of cake:
Some cakes have frosting; others have icing.
- The plural of fruit is fruits, but only when you're talking about different varieties:
Some fruits -- bananas, apples, kiwis -- are good for you. The rest are not.
You always eat some fruit.
- Drinks are the typical nonountable nouns, except when you're talking about varieties or individual servings:
Whiskeys are either blended or single-malt.
Give me two whiskeys, two scotches, two beers.
Waters has an additional plural as the naturally occurring water in a location, so during your vacation, you
take the waters at the spa at the hot springs
- Cheese follows the variety rule. If you have three cheeses on your cheese plate, then you have three different types of cheese, even when you have six pieces of cheese total. Same with milk:
I make three different nut milks in my blender -- walnut, hazelnut, and almond.
The plural of beef is beeves, but it's only used to describe individual animals, meat-on-the-hoof, so to speak.
Best Answer
Your actual garbage disposing action is picking bags or packs or containers with garbage. Consider these:
The only thing I know that can be a countable piece of trash is a disposable. Disposables are diapers, syringes, cartridges, etc.