は
wa
Put up a sign before you speak: は
The picture Standing a small sign in front of your sentence: this is what we are talking about now. Whatever is not on the sign quietly stays outside. は stands up a sign for what you are talking about; が points a finger at one thing.
Where the picture shows up in は
-
the sign you put up
私は今日夜勤です。
watashi wa kyō yakin desu
I'm on the night shift today.
A small sign reading 'me' planted on the desk, with tonight's shift written in behind it
-
two signs at once
コーヒーはありますが、牛乳はありません。
kōhī wa arimasu ga, gyūnyū wa arimasen
We have coffee, but no milk.
Two signs stood side by side — a cup sitting under one, bare table under the other
-
the one we both know
その書類は課長が持っていきました。
sono shorui wa kachō ga motte ikimashita
The section chief took that document.
A finger pointing at the document already lying on the desk as a sign goes up beside it
-
moving the sign
今日は早く帰ってください。
kyō wa hayaku kaette kudasai
Go home early today.
Pulling up the sign that stands there every day and planting it again on the square marked 'today'
-
a sign over the whole thing
日本は夏によく雨が降ります。
nihon wa natsu ni yoku ame ga furimasu
In Japan it rains a lot in summer.
One wide sign staked across the whole map of Japan, with summer rain drawn in underneath
は for what is always so, が for what you notice right now. Looking out the window you say 雨が降っています.
All of it in one picture
は is one signboard. Put yourself on it and tonight's shift follows behind; stand two of them up and coffee and milk fall to opposite sides. Plant one on the document you both already know and it becomes 'that document — here's the thing', and move the same sign onto 'today' and today gets ruled off from other days. Stake it across all of Japan and you are talking about how things always are. Whatever comes after は is the answer to that sign.