True.

And the same is true of all other things; they have each of them an end and a special excellence?

That is so.

Well, and can the eyes fulfil their end if they are wanting in their own proper excellence and have a defect instead?

How can they, he said, if they are blind and cannot see?

You mean to say, if they have lost their proper excellence, which is sight; but I have not arrived at that point yet.

I would rather ask the question more generally, and only enquire whether the things which fulfil their ends fulfil them by their own proper excellence, and fail of fulfilling them by their own defect?

Certainly, he replied.