As a native Japanese speaker, I often find many Japanese learners being so much confused with the difference between particle が and は. Some learners highly recommend Tae Kim’s Japanese Grammar Website. But his article about が and は isn’t so good, unfortunately. (Note: I’m not denying all of his articles because I haven’t read through them all yet.)
From different points of view, I explained about the difference on several pages including on external websites. Let me compile them here as an alternative guide for you.
Nutshell:
が is for a vertical comparison whereas は is for a horizontal comparison when they are preceded by a subject.
→ Read this discussion first.
Example sentences with explanation:
- What’s the difference between この鍋は鉄でできています and この鍋が鉄でできています (both means “this pot is made from iron”)? answered on HiNative
- What’s the difference between 私は毎日、部屋の掃除をします and 私が毎日、部屋の掃除をします (both means “I clean up the room(s) everyday”)? answered on the same page of the first case.
- What’s the difference between 我が社では車を作ります and 我が社が車を作ります (both means "our company makes cars)? answered on HiNative – Hint: it’s a looooong series of threads. Jump to my answer posted on Feb 9, 2021.