The wikipedia entry for "Primum non nocere" mentions that it's sometimes written as "Primum nil nocere".

I realize the shade of difference is probably pretty fine, but is one of these more correct?

2 Answers 2


Prīmum nōn nocēre means "first, to not cause harm". Nōn negates the verb.

Prīmum nīl nocēre means "first, to cause harm to nothing". Nīl is the object of the verb.

(Note that both are infinitives rather than commands in Latin; the original context is something like "the first law of medicine is to not cause harm".)


It's possible that nil is a noun here, but it's more likely that it's the adverbial nil, which would translate to something like "not at all."

B. Adverb. 1. Not (as a strengthened non), in nothing, in no respect, not at all: “me nihil poenitet,” Plaut. Bacch. 5, 2, 63 (etc.)

So the difference between the two would be the strength of the negation. In English, you can hear the difference between these two statements:

  1. Don't do it.
  2. Don't even think about doing it.

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