Here's a brief introduction of は vs が. が marks the subject ("subject marker") of a sentence like in other languages. - くるまが くる: A car is coming. (no special connotation but a simple factual statement) は is "topic marker", but it often doubles up as the subject of a sentence as well. When the subject is marked with は, it has the connotation of expounding it, drawing the listener's attention to say more about it. - わたしは せいとです: I am a student. (a nuance of a new discourse on わたし with more to come) は can also start a compound sentence which employs a full [subject+predicate] clause. - わたしは せが たかい: As for me, my stature is high (describes わたし using a full clause せが たかい) (わたし: topic as well as subject of main clause, せ: subject of subordinate clause) To say the same thing in English, one would use "As for me, ..." which starts to talk about "me". So we can say が brings focus to the noun it marks, while は directs attention to what comes after it. は is often used to make a statement of contrast. - かれは がっこうへ いったが わたしは いえに きた: He went to school but I came home. The topic and subject marker can also work together to form a sub-main compound statement. - かれが きた とき わたしは ねていた. When he came, I was sleeping. (typical subordinate and main clause arrangement: が in sub-clause, は in main) In a discourse, が tends to introduce a new subject, which corresponds to the use of indefinite article "a" in English. は statement(s) then says more about the new subject, as one would do using the definite article "the" in English. 1. 昨晩火事が起きた: A fire broke out last night. (が corresponds to "A") 2. その火は大きな被害をもたらした: The fire caused a great damage. (は to "The") (#1 introduces a brand new subject, a fire, and #2 gives more detail about it) So one can say は takes the center stage, and が has a supporting role.

Hi Iwan, I wrote a blog post about it here. http://www.japaneserabbit.com/#!は-or-が/c218b/561ad7130cf2c3576e58661a Hope it helps.

I've been doing Japanese for like 4-5 years now and I know i could not explain any of better than a lot of them out there. My advice as long as you generally get the meanings is to not dwell too much on it. A feel for which is used when will come over time from exposure content reading/hearing sentences seeing when natives use which when etc.