I'm having a hard time translating this phrase from Caesar's De Bello Gallico. I understand, from doing a bit of research, that probat illis introduces indirect speech.

Perfacile factu esse illis probat conata perficere, propterea quod ipse suae civitatis imperium obtenturus esset:

(De Bello Gallico, Book I, Chapter III, Section V)

So far I have, "he proved to them that completing these efforts was done very easily". But why is factu in its peculiar form? I would expect a past participle, factum, which would agree with the case, gender and number of the infinitive perficere. I don't understand the -u ending of factu.

Thanks for any help!

2 Answers 2


Perfacile factu means "easy to do." Factu is a supine, and this construction—supines coming off of certain adjectives—is pretty much where you will always see its ablative form. Other common examples are:

  • Mirabile dictu, "Amazing to say";
  • Difficilis latu, "Difficult to bear";
  • Optimum factu, "Best [thing] to do;
  • Nefas dictu, "Unlawful to say".

With that in mind, rearranging the sentence to meet English syntax we get:

Probat illis perficere conata esse perfacile factu.

"He proves to them that to complete these efforts is easy to do."

  • 2
    Worth mentioning (as you implicitly do here) that the ablative supine is really only common with certain words.
    – brianpck
    Commented Nov 29, 2016 at 3:06

Your translation "he proved to them that completing these efforts was done very easily" is good. To express such things in Latin the supine is a good choice. The supine ablative (like factu) is an ablative of respect. For example:

Hoc responsum facile est scriptu.
= This answer is easy with respect to writing.
= This answer is easy to write.

If something (this answer) has a property (easy) regarding the action of some verb (to write), the usual Latin choice is to use an adjective with the supine ablative. In your example, if I drop the ACI structure, we have:

Perficere perfacile est factu.
= Completing is easy with respect to doing.
= It is easy to complete.

Essentially perfacile factu means "easy to do", but it is better to understand the structure than to learn it as an isolated phrase.

Notice that the supine is not the same thing as the (passive) perfect participle. The participle has first and second declension endings, whereas the supine is fourth declension. The supine is formed from the same stem — at least a stem that looks exactly the same — as the participle, and it is important to be able to distinguish between the two. For the ablative it is easy, but the supine accusative looks exactly like a participle. The supine has no other cases.

  • I have one question, which might be nitpicking, but will help it make more sense to me. Since the past participle (supine) is passive, would it technically be "This answer is easy with respect to being written"?
    – ktm5124
    Commented Nov 28, 2016 at 22:46
  • @ktm5124, the perfect participle is not the supine. They are two different things. I will add this to the answer.
    – Joonas Ilmavirta
    Commented Nov 28, 2016 at 22:47

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