I don't understand why my は was changed to a に when a native corrected my sentence


> My sentence: 彼はこれを出来るなら僕は矢っ張り出来る
>
> Correction: 彼にそれが出来るなら、僕にもできる

I can understand the rest of the changes, but why はー＞に ? All they said was
that it sounded more natural but they weren't sure why. Could someone explain
this to me? Thanks!




tl;dr: 「は」 is a big no-no for the subject marker in if-clauses.

A two-step explanation will be in order here.

First, there is a big grammar rule that says " **DO NOT use 「は」 as the subject
marker in an if-clause. Use 「が」 for that**."

Correct:「キミ **が** 行{い}くなら、ボク **も** 行く。」

Incorrect:「キミ **は** 行くなら、ボク **も** 行く。」

This seems to be a very common mistake among Japanese-learners. SE is no
exception at all.

Secondly, 「できる」, which is used in your sentence, is a special verb that can
take 「に」 with the subject as in 「(person) + に + できる」. However, the が-over-は
rule for the if-clauses still stands, which is why it is **incorrect** to say:

> 「彼 **は** できるなら、ボク **は** やっぱりできる。」

which is essentially what you wrote.

That is because the first part of that sentence is an if-clause as it uses
「なら」. You just cannot use 「は」 there. Thus, it is only **_correct_** to say:

> 「彼 **が** できるなら、ボク（に）もできる。」

But as I mentioned above, it is more natural to use 「に」 than 「は/が」 with 「できる」.
Thus, your teacher/friend corrected your sentence that used 「は」 to:

「彼 **に** それ **が** 出来るなら、僕 **にも** できる。」




tl;dr: 「は」 is a big no-no for the subject marker in if-clauses.

A two-step explanation will be in order here.

First, there is a big grammar rule that says " **DO NOT use 「は」 as the subject
marker in an if-clause. Use 「が」 for that**."

Correct:「キミ **が** 行{い}くなら、ボク **も** 行く。」

Incorrect:「キミ **は** 行くなら、ボク **も** 行く。」

This seems to be a very common mistake among Japanese-learners. SE is no
exception at all.

Secondly, 「できる」, which is used in your sentence, is a special verb that can
take 「に」 with the subject as in 「(person) + に + できる」. However, the が-over-は
rule for the if-clauses still stands, which is why it is **incorrect** to say:

> 「彼 **は** できるなら、ボク **は** やっぱりできる。」

which is essentially what you wrote.

That is because the first part of that sentence is an if-clause as it uses
「なら」. You just cannot use 「は」 there. Thus, it is only **_correct_** to say:

> 「彼 **が** できるなら、ボク（に）もできる。」

But as I mentioned above, it is more natural to use 「に」 than 「は/が」 with 「できる」.
Thus, your teacher/friend corrected your sentence that used 「は」 to:

「彼 **に** それ **が** 出来るなら、僕 **にも** できる。」

