There are research techniques where something is investigated under working conditions, and these techniques are commonly referred to as in situ.

For the sake of being specific to my field of study, investigation of electrode material in situ is when the material is studied in the battery that has been put in some static condition (constant voltage applied and the battery cell is in equilibrium).

Lately, there is a novel term, "operando," which is a more specific "in situ." It is a method for studying electrode material in a working cell while the system changes under an external influence. For example, while the battery charges under constant current.

Roughly speaking, in situ is for studying the state, operando is for studying the process.

The question is: should "operando" or "in operando" be used?

I tried following the literature to avoid being wrong, but it does not help much. For example, Wikipedia has an article on operando spectroscopy, and there is no "in" anywhere in the article. There is also no "in operando" page on Wiktionary, only "operando". However, in research papers things get messy and there is extensive use of "in operando", e.g., here, here, and here. And there is also a lot of "operando" e.g., here, here, and here. So, even within Nature journals, there is no clear agreement. Is there a correct way? Does it matter at this point, or now it is just a matter of personal preference?

  • Hi, Alexey. I searched the edits for this Wikipedia page's history and found a note from an editor in 2016 removing the incorrect use of "in operando." In my opinion, the use of "in" with that word is an error and an artifact of its juxtaposition with "in situ."
    – rolfedh
    Commented Jun 20, 2020 at 10:28
  • Yes, looking at the edits, the Wikipedia article contained the phrase, "Frequently the term "operando" is mistakenly written as "in operando", which is incorrect use of the Latin language." However, this was removed in a later revision.
    – rolfedh
    Commented Jun 20, 2020 at 10:37
  • One contributor at Reddit_Rt Chemistry seems to rank 'operando' and 'in operando' as no more than style variants: 'There was a conference on this a few years back to normalize the nomenclature. All in operando measurements are in situ, but not all in situ measurements are operando.' Expecting readers to pick up a very subtle distinction between 'operando' and 'in operando' from this text, without explanation, would contravene Grice's axiom of clarity. Commented Jun 20, 2022 at 14:07

2 Answers 2


I would expect "operando" (no "in") to be the correct form.

My Latin is a bit rusty, and this technical use of operando is new to me, but we can break down the grammar. (Magistri, please correct any dubious details in the comments!)

Operando is a gerund, i.e., a verbal noun, recognizable by its form. Gerunds often get translated into English with "-ing" gerunds, in this case "operating" or "running".

The o ending and context indicate that it is in the ablative case, which is a messy, multipurpose category for oblique functions often expressed with prepositions in English. It would be accurate to translate "operando" as "in operation" or "while running" or similar, but this form and meaning do not require the use of a preposition in Latin.

In contrast we have many phrases that use Latin nouns in the ablative to convey a similar concept (the technical means by which something is accomplished), but they often appear with the preposition "in". Why? Those phrases usually are expressing a physical (or figuratively physical) location or state in which something is accomplished (in vitro fertilization, in situ conservation, in loco parentis). For those functions and forms, Latin does use a preposition.

I hope that helps!


As far as I am concerned, operando does not need an "in", which denotes a place. While operating is the correct translation of this gerund form. Even though Operando Microscopy is being used and it is confusing because actually, in situ is meant.

  • 2
    Hello, Luis. Answers on ELU are rarely considered satisfactory if they are not supported by credible references, linked and attributed. // As a counter-argument, in situ is licensed by respected dictionaries as having become fully integrated into the English lexis (a loan from the Latin, of course). 'In my opinion' uses a sense of 'in' (if you analyse the PP rather than accept it as an idiom) far removed from the prototypical locative sense. Commented Jun 20, 2022 at 14:02

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