1. I like pears, too.

2. I like pears too.
3. I like pears, as well.
4. I like pears as well.
5. I don't like pears, either.
6. I don't like pears either.
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1,2,5,and 6 are grammatical, aren't they? How about #3? There is a comma before 'as well.' Is this expression correct?

1, 3, 5 - correct.

4 can be considered correct, too, depending on the meaning.

Yes, expressions 1, 2, 5, and 6 are all grammatical. They convey the same meaning, which is the speaker expressing their liking or disliking for pears.

Regarding expression #3, "I like pears, as well," it is grammatically correct, but it has a slightly different meaning compared to the other expressions. In this case, the speaker is using a comma to set off the phrase "as well," which adds extra emphasis to their liking for pears. It indicates that the speaker not only likes pears, but they also like something else mentioned previously. For example:

Person A: "I like apples."
Person B: "I like pears, as well." (meaning they like both apples and pears)

So, while expression #3 is correct, it conveys a slightly different meaning compared to the other examples without the comma.