The meaning and tense of できるはず in this passage


A and B were involved in negotiations. A was in a superior position, but there
was one and new unfavourable condition that if B knew about, would put A in a
huge disadvantage. This was kept secret and agreement has been made.

The story was casually retold in Kansai-ben:

> 誠に楽な条件でええ塩梅に協定ができた。  
>  それ、 **できるはずや** 。 「description of the unfavourable
> condition」のにそれをおくびにも出さずにやったからです。

I assume dialect is irrelevant here and the speaker would make it できるはずだ in
hyōjungo. From the context I guess it is used to mean something like "it
couldn't have failed" (because the disadvantage was kept secret) rather than
"be able to".

What I am confused is the discrepancy in tense here: できた - はずだ - やった. Why
wasn't it できるはずだった?

Is it a more general statement? Like "it always works out if you keep your
mouth shut"?




In short, できたはず or できるはずだった would imply you failed it. e.g.

  * どうしてやらなかったのだろう、やればできたはずだ。 Why didn't I do it? I could have done it if I had tried.
  * 昨日までにできるはずだった。しかし、今日までかかってしまった。 It should have been made by yesterday. But it took till today.

And, how you consider the できるはずだ a general statement seems apt.

As for できたはずだ, depending on intonation, you can express your first
interpretation i.e. "it's natural that you could" by pronouncing it as two
phrases of できた and はずだ with ~~their own pitch patterns alive~~ regaining raise
of pitch i.e. [できた]{HLL} [はずだ ]{LHHL} opposed to normal [できたはずだ↓]{HLLLLL}

(できた1 はず0 だ1)




In short, できたはず or できるはずだった would imply you failed it. e.g.

  * どうしてやらなかったのだろう、やればできたはずだ。 Why didn't I do it? I could have done it if I had tried.
  * 昨日までにできるはずだった。しかし、今日までかかってしまった。 It should have been made by yesterday. But it took till today.

And, how you consider the できるはずだ a general statement seems apt.

As for できたはずだ, depending on intonation, you can express your first
interpretation i.e. "it's natural that you could" by pronouncing it as two
phrases of できた and はずだ with ~~their own pitch patterns alive~~ regaining raise
of pitch i.e. [できた]{HLL} [はずだ ]{LHHL} opposed to normal [できたはずだ↓]{HLLLLL}

(できた1 はず0 だ1)

