The usage of ば is complicated.

If volition / request / etc is involved, the sentence is invalid, unless there
are special conditions fulfilled (addressed after this example):

> X 卒業すれば、彼女と結婚するつもりです。(volitional structure つもりです)

Usage of such volitional structures is allowed under two circumstances:

  1. If the subjects (主語) of the two sentences are different:

> O 彼女が希望すれば、彼女と結婚するつもりです。(subjects are 彼女 and わたし (implied))

  2. If the verb is not an action verb (adjective, stative verb, etc):

> O わからないことがあれば、わたしにきいてください。(あれば stative verb, as it expresses the state of
> being)
>
> O 質問があれば、(あなたが)聞いてください。(あれば stative verb)

These two conditions can be found in various materials, such as [the top
answer to the question in this
link.](https://japanese.stackexchange.com/questions/393/differences-
among-%E3%81%9F%E3%82%89-%E3%81%AA%E3%82%89-%E3%82%93%E3%81%A0%E3%81%A3%E3%81%9F%E3%82%89-%E3%81%88%E3%81%B0-etc)

> "The main clause must be a constant non-volitional reaction to the
> conditional clause unless the conditional clause shows state or if the
> subjects of the two clauses differ."

This much information can be found in various materials. However, I noticed
that when rule 2 applies, the subjects are often automatically different (i.e.
rule 1 is applied too). **What if adjectives / stative verbs are used when the
subjects are the same?** (note: example sentence below has been edited from
声をかけてください)

> ？ (あなたが)そこにいれば、(あなたが)何か言ってください。(eg. when on the phone)
>
> ？ (あなたが)そんなに悲しければ、(あなたが)帰ってください。
>
> ？ (あなたが)ひまであれば/なら、(あなたが)てつだってください。
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question
grammar conditionals
Usage of ば - is あれば...ください valid when the two subjects are the same?
~~Edit: I now doubt my answer is correct.~~ (Never mind)

In the first place, the explanation above seems not accurate to me. The reason
why わからないことがあれば、わたしにきいてください is accepted is not because the predicate is static
or whatever but because わからないことがある is not a volitional action of the same
subject of the main clause. So, when static verbs are used when the subjects
are the same as you ask, it can be still ungrammatical as long as the verbs
stand for a volitional action. In this regard, そこにいる is done at your will, so
(あなたが)そこにいれば、(あなたが)声をかけてください is odd.

On the other hand, 悲しければ帰ってくれ and ひまであれば手伝ってくれ are fine because 悲しい and 暇である
are not your volitional action.

In summary, this structure doesn't work when both the conditional clause and
the main clause are penetrated with volition by the same agent.
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