Can I say?
If we are talking in general, we can say:
- The dolphin is an intelligent animal.
- A dolphin is an intelligent animal.
- Dolphins are intelligent animal.
- The Vietnamese are white.

So if we are talking in general, can we say:
1 I don't like the dolphin.
2 I don't like a dolphin.
3 I don't like the Vietnamese.

I know that we can say "I don't like dolphins."

Thank you for your help!

Question

Can I say?
If we are talking in general, we can say:
- The dolphin is an intelligent animal.
- A dolphin is an intelligent animal.
- Dolphins are intelligent animal.
- The Vietnamese are white.

So if we are talking in general, can we say:
1 I don't like the dolphin.
2 I don't like a dolphin.
3 I don't like the Vietnamese.

I know that we can say "I don't like dolphins."

Thank you for your help!

Answer

I think your question refers to when we use the definite and indefinite article.

For example 1: 'I don't like the dolphin'.  This would normally mean I don't like a specific dolphin I saw in the sea.  As a general rule,  we use the definite article 'the' to refer to something specific that we already know about or can identify.
However, when we talk in general we don't usually use the indefinite article 'a'. So the correct way to say example 2 would be 'I don't like dolphins; because you are talking in general.
With example 3, it is correct. 'The Vietnamese' refers to a group of people.

If you need further explanations on articles please book a lesson with me.