different matter; separate issue; another question
Used to assert that something is unrelated to the current topic, or should be treated as a distinct case. Often appears in phrases like それは別問題だ (that's a different matter).
Whether you have the ability and whether you have the motivation are separate issues.
彼の意見は面白いが、それが正しいかどうかは別問題だ。
His opinion is interesting, but whether it's correct is another question.
Having ability and having motivation are two separate matters.
Setting the cost aside as a separate matter, let's first examine the idea.
Even if it's legal, it becomes a separate issue morally.