A は vs が question

[jkid]

I know it is very difficult to explain when to use which particle when looking at は/が but please try.

Today I encountered the ています construction relating to intransitive verbs and expressing a state resulting from the verb. I then looked at making something a topic with は while incorporating this construction (up until this point was introduced が had been used in all the examples).

This example was provided for using は:

*CANT CONFIRM IF THIS SENTENCE IS 100% CORRECT RIGHT NOW BUT HOPEFULLY YOU GET THE IDEA *

このエレベーターはこわれています。

My 先生　said using が in the above sentence is correct grammatically but implies you are "trying to to find out which elevator is broken" and to use が context is required. I don't fully understand how using が vs は changes the meaning in this way. I could understand if you could only use は in the above example and が could only be used when asking or responding but it seems that is not the case.

Well, I hope everything I said above makes some sense. I really need clarification on this point.

[Javizy]

You should look more closely into the definition of topic, since this is really what it's all about. Among other things, anything that can be directly perceived by both listener and speaker, with their five senses alone, is marked by は. If you say 'this elevator', I know exactly what you're talking about, because it's immediately visible, so it is marked with は, or more often than not omitted completely.

Another way of thinking about the difference, is as an answer to an unasked question. In this case:

このエレベーターは、どうした
このエレベーターは、こわれている
As for this elevator, what's wrong with it?
As for this elevator, it's broken.

どのエレベーターがこわれている
このエレベーターがこわれている
Which elevator is broken?
This elevator is broken.

As you can see, は throws the emphasis on what follows, since we already understand what it marks, が, on the other hand, puts the focus on what comes before it. Both of the answers would be more naturally translated as simply 'this elevator is broken', but you should be able to see that there is a difference in meaning in the Japanese, which fits in with what your teacher said.

[hatch_jp]

Please refer to the following site.
http://japanese.about.com/library/weekly/aa051301a.htm

[jkeyz15]

Your sentence sounds like it's answering the silent-question:
どのエレベーターが壊れていますか？

[jkid]

Thanks all for your responses I now understand what's going on.

[gerald_ford]

Please refer to the following site.
http://japanese.about.com/library/weekly/aa051301a.htm

Him this site is pretty helpful. I've been learning Japanese for years, and still often get these wrong (as my wife will tell me). I noticed that "ga" seems to be used in more situations than "wa". Does that sound right?