In al-Haytham's Opticae Thesaurus, the following sentence (discussing what the first book will describe) confuses me:

Primum est quod lux per se et colores illuminati operentur in visum aliquam operationem.

It seems to say (fairly literal transl.) "First is that light by itself and illuminated colors work within the eyes some operation." My confusion is with the use of accusative 'aliquam operationem' which I'm guessing goes with 'operentur', but that doesn't seem to work; and the use of 'in (+acc)' which I understand as 'into' typically, but here I read it more like 'within'. Generally I'm having a hard time reading the sentence correctly, is the syntax unusual? Or is it related to the subjunctive 'operentur'?

1 Answer 1


Operari + accusative object is indeed not classical, but it is found in ecclesiastical Latin, including the Vulgate (and good dictionaries like Lewis & Short mention it). I understand we are looking at a Latin translation of an Arabic text here, which (the translation, that is) was produced in the 12th century, so this does not seem out of place. By the way, the quod + subjunctive (or indicative, as discussed in detail in this question) is a typical feature of ecclesiastic/medieval Latin.

So the colours “cause a working,” or more idiomatically: “produce an effect.”

Next, you take in visum to answer the question "where," but, as you probably know, that is more or less the textbook definition of what in + accusative does not mean. It describes a directed action, so I would rather translate this as “have an effect on,” yielding the full translation:

First, that light by itself as well as illuminated colours produce some effect on the visual sense.

  • Thanks Sebastian. Follow up, when you say "you take in visum to answer the question 'where'... that is more or less the textbook definition of what in + accusative does not mean" do you mean that in+accusative is not used for saying e.g. "within the eyes" like my translation? Or that the author used it in the other way, to imply directed action, despite the classical usage being different? I ask because I thought that with accusative "in" meant "into, toward, within", while in+abl can mean "upon" or "onto". Commented Jun 21, 2022 at 19:45
  • Also, of course English words aren't the best for describing Latin prepositions (or foreign prepositions in general) so I might have misinterpreted. Probably time for me to review LLPSI again and look for examples of both Commented Jun 21, 2022 at 19:46
  • @SamGallagher the accusative denotes motion/direction (to/into), the ablative rest (in). So you say in Italiam venire but in Italia habitare. In (with both accusative and ablative) is frequently used where you would use “on(to)” in English. Commented Jun 21, 2022 at 21:35

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