On the Cavalry Commander (8.1-8.2)

As the horse will frequently have to gallop down hill and up hill and along a slope, and as he will have to leap over, and to leap out, and to jump down at various times, the rider must teach and practise both himself and his horse in all these things. For thus they will be able to help each other, and will be thought altogether more efficient.

If anyone thinks that we are repeating ourselves, because we are referring to matters already dealt with, this is not repetition. For we recommended the purchaser to try whether the horse could do these things at the time of buying: but now we say that a man should teach his own horse; and we will show how to teach him.