nouns

Abstract noun refers to something which has no physical form, something which we cannot see or touch. It often refers to ideas, concepts or feelings. Abstract nouns are often based on the meanings of adjectives and verbs.
brave (adjective) – bravery (abstract noun), know (verb)- knowledge (abstract noun)

Concrete noun is the opposite of abstract noun. Many concrete nouns refer to people, things, animals and places. Other concrete noun refer to substances, liquids and gases

除了abstract noun 和 concrete noun, Nouns 還分 countable noun (可數名詞) 和 uncountable noun. (不可數名詞)

concrete nouns 多數是 countable noun, abstract noun 多數是 uncountable noun. 但是許多例外.
action (countable abstract noun) – actions (plural)
invitation (countable abstract noun) – invitations (plural)

Countable noun 前面可以加數目字, one, two, ten …a/an, many, few
One egg, two eggs, an egg, many eggs, few eggs
One boy, ten boys, a boy, many boys, few boys

Uncountable noun 前面不可以加數目字, a/an
Luggage (u)
two luggages 是錯, 應該 two pieces of luggage

確定 Noun 是否 countable, uncountable 或兩者都可以, 要查看字典
travel (u)
trip (c)
coffee (c, u), experience (c, u)

rate = number of times something happens, 可以數
population = number of people (or animals) living in a particular area
point = number that shows your score in a game or sport
在上面三個 nouns 可以數目表示
population 2 million
Rate 11%
Points 9 out of 10

Evidence 是 uncountable, 不可以用數目表示
two pieces of evidence

Decline 是 uncountable/countable, 多數 uncountable 用, 就算當 countable用, 只是 singular e.g. a decline