有咩方法分個字+S 定 冇S

Noun 可分 countable noun (可數名詞) 和 uncountable noun (不可數名詞)

countable noun 可以很清楚地數得出來, 起碼視覺上可以判斷出來, 一個, 兩個, 十個, 指動物、植物或實體東西.
singular 和 plural . 通常 singular noun + s 便改為 plural noun. 有許多例外字 (man – men, mouse – mice, church – churches, fly – flies, box - boxes, thief - thieves…etc.)

uncountable noun 指某些東西，根本無法數, 多數是 abstract noun (抽象名詞), 例如 love, kindness, patriotism, music 不具體的東西, 或者統稱東西 (iron, gold, rice, water… etc)
uncountable noun 沒有+ s, uncountable noun 多數是單數

這只是 general guideline , 問題英文有許多例外, 有字可以做 countable noun 和 uncountable noun, 真要記. 如果不清楚, 最好查字典. 好字典列出 noun 是countable, uncountable or both. 例如 Longman English Dictionary

countable nouns, 可以用 a, one, two, three,… many, few 在 noun 前面.
e.g. few boys
uncountable nouns, 可以用 much, less 在 noun 前面. 不用 a, one, two three....改為 a piece of advice, three pieces of baggage

Some examples of uncountable nouns:
furniture, information, baggage, luggage, scenery, money, advice, music

There is a hair in my soup. (one single hair ~ countable)
You have black hair. (all the hair on your head ~ uncountable)

You can stay with us. There is a spare room. (a room in a house ~ countable)
You can’t sit here. There isn’t enough room. (room = space ~ uncountable)

補充一下

如果英文最後一字是響音字（a，e，i，o，u）
那麼要加 es

如果英文最後一字是 y
必須把 y 轉成 i
然後才加es

很抱歉。真系要死記。