What's the meaning of the ending じゃないの?

Question

I found it twice. First in a song:

いつもその本はハッピーエンドじゃないの。

And then the title of a manga:

遊びじゃないの。

じゃない alone is for negation (no happy end, no playing). What I can't understand is the の at the end of the sentence... what does it stand for?

Answer 1

Is ending question sentences with の really feminine?

の(だ)/のです with a rising tone are the abbreviations of の(だ)か/のですか。

(The combination だか isn't really used in everyday life to the best of my knowledge).

They turn the sentence into a question which, combined with じゃない make it a tag question, as you can see in the links I posted in my comments.

遊びじゃない？ 遊びじゃないか。 遊びじゃないの（か）？

It's a game isn't it? It's a game right? You're playing aren't you?

Without the rising tone (or か), じゃない is used to deny what precedes it. の/のだ/のです　have many different meanings (look it up on this site), the most common ones being adding an explanatory and/or exclamative tone to the sentence.

遊びじゃないの（だ）。遊びじゃないのです。

It's not a game. It' not a game! (What the hell are you doing, ) it's not a game! (I can't believe you take it so lightly, ) it's not a game (you know?).

The sentences in の are often used to answer the implicit question "What is happening?" : "Well, what's happening is..."

誰かが来た？ (Gathering information after coming home).

Someone came?

誰かが来たの？ (Seeing 2 cups of coffee on the table).

(What happened,) someone came?

I don't feel comfortable enough with those grammar to go further into details, I would advise you to look for informations about the differences between だ/です VS の（だ）/のです and （だ）か/ですか VS の(だ)か/のですか.

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EDIT : Just to be clear, here are the different forms :

Simple　　　　　　　　　Abbreviated　　　　　　　　　Using の　　　　　　　　　Abbreviated using の

猫だ。 　　　　　　　　　猫。　　　　　　　　　　　　　　　猫なのだ。　　　　　　　　　猫なの。

猫です。　　　　　　　　　　　　　　　　　　　　　　　　　猫なのです。　　　　　　　

猫（だ）か。 　　　　　　猫だ？/猫？　　　　　　　　　猫なの（だ）か。　　　　　　猫なのだ？/猫なの？

猫ですか。　　　　　　　　　　　　　　　　　　　　　　　　猫なのですか。　　　　　　猫なのです？