Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
Explain the main differences between abstract and concrete nouns.

### Response:
Abstract nouns are intangible concepts, such as an emotion, quality or state. They cannot be seen or touched. Concrete nouns, on the other hand, represent tangible things that can be observed and experienced. Examples of concrete nouns include people, places, and things. Abstract nouns are often used to describe abstract qualities of people, things, or ideas. They can also be used to describe intangible ideas, such as freedom or justice. Concrete nouns, meanwhile, are most often used to describe tangible or physical items.