This question is partially open ended.

I'm looking for a Latin idiom or euphemism or phrase that expresses something being from or related to practice as opposed to being related to theory. Something that was practiced or developed or is otherwise related to being "in combat" as opposed to "on paper". Surely the Romans had a distinction for this with their love of heuristic and difficult numbering system.

I'm not asking for a translation for "in combat" or any host of English phrases that suit this purpose, or anything specific, I'm wondering if there is a more general Latin expression for this.

This seems like something that we surely have inherited a Latin phrase for in modern speaking like "Sine qua non" or "Cui bono". Does this phrase exist in the modern lexicon of adopted Latin expressions? If it's not something that exists in the aforementioned, what would or could it be?

The way I would like to use this Latinism would fit well into the sentence:

"Our tactics were tested and refined in the field after we implemented them in training exercises"

  • Welcome! Thanks for contributing. If you have a particular context in mind, of how you would use this expression, that might be worth including in your question as well. May 18, 2016 at 2:07
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    Just making sure: de jure vs. de facto aren't what you're looking for, are they? The difference between something being official on paper and something being true in fact (e.g. "In many places in America there's still de facto segregation even if there's no de jure segregation any more")? May 18, 2016 at 11:23
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    @JoelDerfner no, that is not what I am looking for. De jure and de facto draw a similar distinction but they do not communicate this particular one, which is closer to the distinction between stress tested vs. non-stress tested, rather than "on the books" vs. in reality. I will add this to my quesiton. The English phrases that I have in mind have a flexibility that I'm hoping to capture. I could be asking for too much. Otherwise your answer is acceptable for many uses.
    – Valerie
    May 18, 2016 at 13:47
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    The closest I can find so far is exercitatio, -onis and usus, -us (as in usus est magister optimus, practice is the best teacher)
    – Rafael
    May 18, 2016 at 13:58
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    Can you refine your question? A couple ambiguities: 1) under fire/duress (title) is not the same as tested and refined (example), 2) do you want a Latin translation or some Latin phrase that is preserved in current English usage?
    – brianpck
    May 18, 2016 at 15:30

1 Answer 1


I would use the verb probare, which means things like "to test", "to esteem as fit", and "to approve for service". It clearly has the tone "to test in practice" as opposed "to esteem highly without really testing". If you have build a machine and tested it in practice, I would refer to it as machina probata.

I would simply use probare and the participle probatus for things like you propose. If you want to emphasize that something was tested in a specific way — literally or not — to add more flavor, I would add an ablative of means. For example, to test a machine in battle is machinam proelio probare. For a slightly different tone, you can consider in proelio (in battle) or per proelium (through battle) instead of proelio (by battle). Proelium is not the only thing you can test with; there are options like ignis, durum, and labor.

I have not encountered a Latin idiom having the same effect as "tested under fire", but igne probatus will certainly be understandable in suitable context.

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