は vs が & 石 vs 右 kanji: 120/2042

Before I started my Rosetta Stone lesson for today, I did some reading the /r/LearnJapanese. There was a post asking for help with は vs が. Anyone new to Japanese will soon encounter Japanese particles. Particles function similar, but not exactly like, prepositions in English. They help identify where an action is taking place where someone is going to, who said what, etc. They are tough to grasp at first because there is no English equivalent and depending on the usage of preposition may change which particle you will use in Japanese (for example, playing a game in a house and living in a house will use て and に respectively even though they are both translated as "in").

は and が are perhaps the trickiest to grasp and even more so to explain. I know that が is supposed to be used for the subject of the sentence and は is supposed to be for used for the Topic of the sentence. The problem lies in English not really having an equivalent to a Topic. The first comment to the post mentioned before links to this article. Let me tell you, I have read many explanations of how and when to use は and が and this article was the best.

I thought I had it covered until today's grammar lesson in Rosetta Stone.

あなたは鍵がいりますか
vs.
あなたは鍵を持っています

"You need the key?" and "You have the key." Why did the key become the subject in the "need" sentence but an object in the have sentence? Does the key produce the desire within the topic maker? I dunno.

Today's Kanji were fairly easy. 石 vs 右 threw me for a loop though. 右 is right and 石 is stone. They look pretty close. 石けん is soap. So I was thinking soap had something to do with the right hand or something. Turns out 石けん is from 石鹸 (also means soap) which is something like salty stone. So I just need to remember that 右 has a line at the top.