This is a tough and interesting question. I'll explain radically. *** What is 'は'? (it does't indicate subject) 私はAKIです。(I am AKI) 私がAKIです。(I am AKI) Two sentences look like same.but gramatical structures are completely different. ------------------------------------------------------ *** 私がAKIです。(I am AKI) Very roughly saying, the structure is like this: 私が（I as subject) AKI (AKI as object) です （am as verb) OK, let's suppose '～が' is subject. ------------------------------------------------------ *** 私はAKIです。(Me, it's AKI) 私は is not subject. if you regard ～は as subject, you cannot explain the following sentences. - 「象は鼻が長い」（The elephant has a long nose) which is subject, 象？ 鼻？　 - What's your order? -> 「僕はコーヒー」 　　　（hey, you are a human, not coffee !) - 「あいつは殺す」 　　this means, in 98% case, "I/We'll kill him" very rarely means "He kills" ※ if you say「あいつが殺す」, this 100% always means "He kills" - 「男は度胸、女は愛嬌」 　　means: "it's important for men to have courage, for woman, loveliness.", but Men __is not__ courage. Men is creatures and courage is a state of mind. ------------------------------------------------------ *** Then What is 'は'？ One of the functions of 'は' is 「提題」"to raise the theme/issue of the sentence/conversation". Clumsily saying, it means "talking about" - 「象は鼻が長い」 -> Talking about the elephant, it has a long nose - 「僕はコーヒー」 -> Talking about me, it's coffee (I'll order a cup of coffee) - 「あいつは殺す」 -> Talking about him, it's to kill (I/We will kill him) - 「私はAKIです」 -> Talking about me, it's AKI(My name is AKI) +++ 応用（application) 「僕はコーヒー、あいつは紅茶」 　　　-> Talking about me, it's coffee. And him, it's tea. 「あいつは殺すが、お前は生かす」 　　　-> Talking about him, it's to kill. But you, it's to let live. 「私はAKIで、彼はKIM」 　　　-> Talking about me, it's AKI. And him, it's KIM 「男は度胸、女は愛嬌」 　　　-> Talking about men, it's courage, while women,loveliness. (to be continued)