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According to the Crash Course Philosophy video today, George Berkeley summarized his empirical philosophy with the phrase "esse est percipi", to be is to be perceived. However, it feels somewhat incorrect to use infinitives this way. "Cogito ergo sum", I think, therefore I am, uses present singular. If "seeing is believing" were to be translated, it feels like it should use gerunds, although it could be converted to "to see is to believe", which sounds more awkward. So then, why infinitives in this case?

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just to clarify, I didn't mean that cogito ergo sum is translated as "seeing is believing". – ws04 Mar 16 at 3:59
Thanks for the update. I updated my answer a bit. – Joonas Ilmavirta Mar 16 at 4:01
Apparently the Crash Course Philosophy video is incorrect! From the Wikipedia entry on Berkeley: "In Principles #3, he wrote, using a combination of Latin and English, esse is percipi (to be is to be perceived), most often if slightly inaccurately attributed to Berkeley as the pure Latin phrase esse est percipi. The phrase appears associated with him in authoritative philosophical sources, e.g., 'Berkeley holds that there are no such mind-independent things, that, in the famous phrase, esse est percipi (aut percipere) – to be is to be perceived (or to perceive).'" – Joel Derfner Mar 16 at 5:43
jeez, how do I accept just one of these two great answers... – ws04 Mar 16 at 5:55
I have faith in you! – Joel Derfner Mar 16 at 15:07
up vote 8 down vote accepted

The expression esse est percipi is grammatical. Notice that the gerund does not have a nominative form at all. If you want the corresponding nominative (or accusative when there is no preposition), you need to use infinitive.

The grammatical structure is the same as in giraffa est alta ("the giraffe is tall"). You are simply saying that something is something, and it does not really matter grammatically what these things are. The predicate is est and the subject can be esse just as well as giraffa.

If you want to say "seeing is believing", infinitives are a good choice again. You can say the same thing in English as "to see is to believe" — there might be a slight difference in nuance but the meaning is the same. I would suggest videre est credere. You can't really phrase this as concisely with any other structure.

On the other hand, cogito ergo sum is a very different kind of sentence. It has two clauses and the subject in both of them is the implicit ego.

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Now this is the kind of race I want to see on all questions! – C. M. Weimer Mar 16 at 4:16
@C.M.Weimer, it good to have people racing to answer a new question, but I hope racing doesn't come a priority. I do like an occasional race though, despite you beating me to it by 22 seconds this time... – Joonas Ilmavirta Mar 16 at 14:16

Cogito ergo sum does not mean "seeing is believing". It in fact means "I think therefore I am." Decartes used it as a statement of epistemology: If he can think, if he can conjure up rational process, it follows that he must exist. It establishes the I.

In Latin, there is no nominative of the gerund. What that means is that you'll never see a gerund as the subject of the sentence. Instead, the infinitive is used. A case can actually be made that the infinitive functions as the nominative of the gerund. (It can't actually be the nominative, but essentially they're equivalent.)

Therefore, indeed esse est percipi is fully grammatical.

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Are there any examples in classical latin in which the infinitive is used for the nominative form of the gerund? – ws04 Mar 16 at 4:00
@ws04 Yes, it's all over the place. The most famous, perhaps, is Seneca's maxim Errare humanum est, "To err is human." Publius Syrus' Sententiae contain a number of them. – C. M. Weimer Mar 16 at 4:07
@Publius Syrius Errare humanum est, I feel so good to know that Portuguese Spanish and Italian are so close to latin :), "Errar é Humano" but in this case it's kind of like "Errar Humano é", in English it might not have a closer translation due to the germanic roots, different structure, it's kind of listening to Yoda, "To err human is" - see, weird – Mr. Derpinthoughton Mar 16 at 19:43

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