When to use classifier

Question

Is this sentence grammatically correct? 我吃个苹果。 Or it should be either, 我吃苹果 Or, 我吃一个苹果

Is it correct to use classifiers without any number and demonstratives?

Answer 1

• Is this sentence grammatically correct?

Yes, it is correct. The number "one" can sometimes be omitted before the classifier.

我吃苹果

I eat apples (generally, no specific number or apples implied).

我吃一个苹果

I eat one apple (not two, not half. Number is important here.).

我吃這个苹果

I eat this apple (with the demonstrative, a specific apple).

我吃个苹果

I eat an apple (no specific apple implied, no emphasis on number).

Answer 2

You shall add "了" after "吃" to indicate the action has been completed. Then all sentences make sense as shown below (with or without the classifier):

我吃"了"个苹果

我吃"了"苹果

我吃"了"一个苹果

However, the sentences you have cited are acceptable in the casual conversations below:

Q: 你(想)吃什麼? A: 我(想)吃苹果, or 我(想)吃個苹果, or 我(想)吃ㄧ個苹果. All are fine.

Q: 你(要)吃"幾個"(苹果)? A: 我(要)吃"ㄧ個"苹果.

The examples show that a classifier must accompany the noun if the questioner expects a quantity indicated in the response.