Am I correctly using は and が here.

Question

A friend mentioned that he's sometimes not understood well in English. I thought his English was perfectly OK. I responded,

それはそうだかもしりませんが私があなたの言うことは通じます

Am I using these particles correctly? Or should I have said

それはそうだかもしりませんが私はあなたの言うことが通じます

If the first is wrong, could someone explain what I'm not getting.

Answer 1

You're using the verb 通じる incorrectly. This is an intransitive verb which is used in the form of [language/word] + が/は + [person] + に + 通じる, for example 私の英語が彼に通じる (lit. "My English goes through to him"). If you want to use 通じる, you can say either of:

• あなたの言うことは私に通じます。
• あなたの言うことは私には通じます。

The latter sentence (contrastive は used with に) is more natural in this situation.

If you want to keep 私 as the "subject", the correct verb choice is 分かる. But you may find 分かる tricky at first glance — the standard usage is [person] + は + [target] + が + 分かる. If you're not sure at this point, read this first: Why is it 日本語がわかります instead of 日本語をわかります?

So you can say the same thing like so:

私はあなたの言うことが分かります。

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OK what I've written so far is a dupe answer, but the following part is important.

私 is usually used with は because 私 is almost always in the universe of discourse. But 私 is used with が when:

• So-called exhaustive-listing が is intended
• 私 is in a relative clause (i.e., when 私 is not the main topic of the sentence)

「私があなたの言うことが分かります。」 is also a grammatical sentence, but this sounds a bit funny in this situation. This sounds like "I'm the (only) one who can understand what you say", as if other people were not able to understand him, due to the "exhaustive listing" function of が.

Answer 2

Let's discuss the sentence by breaking it into 2 parts:
それはそうだかもしれませんが and 私(が/は)あなたの言うこと(は/が)通じます.

First Part

それはそうだかもしれませんが

-> Nothing wrong about particles. Good! You should say

それはそうかもしれませんが (removing だ and replacing り with れ.)

to sound more natural. You might find it strange that 知る turns into 知れ when connected to ません (negative,) but it is actually not 知る. It's "知れる."

Second Part

私はあなたの言うことが通じます

almost sounds natural!

Maybe you confused the first は with the one indicating subject.

Let's talk about this using the word わかる.

This 「は」 is originally 「に」. So 私にあなたの言うことはわかります。 is the beginning form. Note that the agent of the action is 私.
Then this 「に」 got 「は」 right after, and an emphasis has been put, which made 私にはあなたの言うことはわかります.
Then 「に」 got omitted. 私はあなたの言うことはわかります. Here, 私, which it the agent of the action, finally looks like a subject.
We got a problem of using 2 or more は in one sentence. So we change the latter は into が because 私 is the agent, which finally makes 私はあなたの言うことがわかります.

So, 私はあなたの言うことがわかります is natural.

But unlike the word わかる, I think it is weird to use 私は with the word 通じる.
When we say that "Somebody understand(s) my language (or words)," we do use the word 通じる. But it's the word that 通じる. Looks like the agent in this case is "the words!" We use it in the same way as わかる, like so:

言葉が 人に 通じる

So you should say:

あなたの言うこと(が/は) 私に 通じます.

And if you add は after に, which makes 私には, you put an emphasis on "私には" (=I can understand....)

So that being said, a little bit of reordering the words makes

私にはあなたの言うことが通じます。

But I don't think you can omit 「に」 in this case because "あなたの言うこと" looks like the agent.

P.S. you can talk about one's English skills as "xxxの英語." So you can also say,

あなたの英語 は 通じます.

Note that there's a difference in nuance between using が and は.
This sentence ends in verb, so は puts an emphasis on the subject where が doesn't.
See this page for details.