So I am having a bit of a confusion with the use of 了. So the teacher gave me a sentence which is this: 我买了两个苹果。 She said that V+了+object requires the object to have specified quantity. After that she gave this sentence: 我买了苹果了 She said that if the object have no specified quantity or information there need to be a 了 after it. I ask her if “我买苹果了” is correct or not and she said it is true colloquially which really baffled me. Can someone tell me where to put 了 in a sentence that have objects but have unspecified quantity (like the one above)
V+了+object requires the object to have specified quantity
No, it is wrong.
The following sentences are all legitimate:
我买了苹果 = I bought apple (not mentioning how many)
我买了两个苹果 = I bought two apples (stating the quantity)
我买了酒 = I bought alcoholic drink (not mentioning how much, not even what kind)
我买了三瓶白酒 = (I bought three bottles of white wine)
 [aspect marker] indicating completed action
 [final particle] indicating change of situation
In all the examples above, 了 is a aspect marker that indicates the action (verb) is completed
我买了苹果了 = I bought apple
我买了两个苹果了 = I bought two apples
我买了酒了 = I bought alcoholic drink (not mentioning how much, not even what kind)
我买了三瓶白酒了 = I bought three bottles of white wine
In all four examples above, the second 了 at the end is a final particle. It serves to emphasize the fact and stress an affirmative tone.
Your teacher said it is colloquial because we do use final particles mainly in speech, but it doesn't mean we don't use it in writing.
我去买苹果(了) = I go to buy apple
我去买酒(了) = I go to buy wine
*You can add final particle 了 to the two examples above (了 stress an affirmative tone - seriously, I am going to buy apple/ wine)*
我买两个苹果 = I buy two apples
我买三瓶白酒 = I buy three bottles of wine
You shouldn't add final particle 了 to the two examples above because they are plain factual statements