Since then a subsistence is necessary in every family, the means of procuring it certainly makes up part of the management of a family, for without necessaries it is impossible to live, and to live well.

As in all arts which are brought to perfection it is necessary that they should have their proper instruments if they would complete their works, so is it in the art of managing a family: now of instruments some of them are alive, others inanimate; thus with respect to the pilot of the ship, the tiller is without life, the sailor is alive; for a servant is as an instrument in many arts.

Thus property is as an instrument to living; an estate is a multitude of instruments; so a slave is an animated instrument, but every one that can minister of himself is more valuable than any other instrument; for if every instrument, at command, or from a preconception of its master's will, could accomplish its work (as the story goes of the statues of Daedalus; or what the poet tells us of the tripods of Vulcan, "that they moved of their own accord into the assembly of the gods "), the shuttle would then weave, and the lyre play of itself; nor would the architect want servants, or the [1254a] master slaves.

Now what are generally called instruments are the efficients of something else, but possessions are what we simply use: thus with a shuttle we make something else for our use; but we only use a coat, or a bed: since then making and using differ from each other in species, and they both require their instruments, it is necessary that these should be different from each other.

Now life is itself what we use, and not what we employ as the efficient of something else; for which reason the services of a slave are for use.