I am searching for a common (though, apparently, relatively obscure) expression that goes something like one of the following:

the crucible of reality
the crucible of truth
the mortar and pestle of reality
the mortar and pestle of truth

The essence is that the true test of something, like an idea, is when it meets with reality and is no longer purely theoretical.

Does anyone know the accurate phrasing of this expression?

  • Maybe you want a phrase that’s not a euphemism.
    – Xanne
    May 28, 2019 at 9:57
  • @Xanne: Maybe euphemism is not the correct term. Maybe it's more like a common, widely recognized phrase used to express an idea. Although, this particular one might be less commonly used than some others.
    – user0939
    May 28, 2019 at 11:58
  • 1
    Did you mean 'aphorism'? Even then that's not really it. 'Idiom' or 'expression' or 'turn of phrase' or 'metaphor'. But definitely not 'euphemism' or 'aphorism'. Those are both misleading.
    – Mitch
    May 28, 2019 at 12:21
  • 1
    @Mitch: I changed "euphemism" to "expression." Thanks. 👍
    – user0939
    May 28, 2019 at 19:19

2 Answers 2


The proof is in the pudding.

which is the very common shortening of:

The proof of the pudding is in the eating.

The idea is that the pudding recipe is the theory, but to know it's a good theory you need to test it in reality, by eating the pudding.

  • I agree "The proof of the pudding is in the eating," is an expression that matches the requirements of the question. Except the phrase I'm seeking specifically contains an object similar to a "crucible" or a "mortar and pestle." Pudding is far enough away in meaning from those two things that I'm sure that phrase is not the phrase I seek.
    – user0939
    May 28, 2019 at 19:24
  • Oh, I see, you wanted something with those actual words or very closely related (high heat or high pressure). The metaphor of a crucible goes in many directions. The most prominent one is not about truth specifically but about quality that survives intense testing (like soldiers "forged through the crucible of bootcamp"). I checked collocates of 'crucible' at COCA and it was swamped with fire and forges and blacksmithing.
    – Mitch
    May 28, 2019 at 21:03
  • That said, looking at entries for the word 'tested' gives something like what I think you want (though no mention of truth directly): "college would be a crucible that tested the strength of all my beliefs.", "aspirational laws can be tested in the crucible of real facts.", "soon to be tested in the crucible of hard times"
    – Mitch
    May 28, 2019 at 21:05
  • "where the rubber meets the road" also fits exactly your title, though not involving blacksmithing or spice grinding skills.
    – Mitch
    May 28, 2019 at 21:07

I would say that the accuracy of a metaphor depends on what it evokes to you and is therefore subjective.
However I prefer 'crucible' or 'proving ground'/'testing ground'.

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