[81] Cicero's distinction, "sordidi quaestus, quorum operae, non quorum artes emuntur," admirable in principle, is inaccurate in expression, because Cicero did not practically know how much operative dexterity is necessary in all the higher arts; but the cost of this dexterity is incalculable. Be it great or small, the "cost" of the mere authority and perfectness of touch in a hammerstroke of Donatello's, or a pencil touch of Correggio's, is inestimable by any ordinary arithmetic. (The best masters themselves usually estimate it at sums varying from two to three or four shillings a day, with wine or soup extra.) True labour, or spending of life, is either of the body, in fatigue or pain, of the temper or heart (as in perseverance of search for things,--patience in waiting for them,--fortitude or degradation in suffering for them, and the like), or of the intellect. All these kinds of labour are supposed to be included in the general term, and the quantity of labour is then expressed by the time it lasts. So that a unit of labour is "an hour's work" or a day's work, as we may determine.[82] [82] Only observe, as some labour is more destructive of life than other labour, the hour or day of the more destructive toil is supposed to include proportionate rest. Though men do not, or cannot, usually take such rest, except in death. Cost, like value, is both intrinsic and effectual. Intrinsic cost is that of getting the thing in the right way; effectual cost is that of getting the thing in the way we set about it. But intrinsic cannot be made a subject of analytical investigation, being only partially discoverable, and that by long experience. Effectual cost is all that the political economist can deal with; that is to say, the cost of the thing under existing circumstances and by known processes. Cost (irrespectively of any question of demand or supply) varies with the quantity of the thing wanted, and with the number of persons who work for it. It is easy to get a little of some things, but difficult to get much; it is impossible to get some things with few hands, but easy to get them with many. The cost and value of things, however difficult to determine accurately, are thus both dependent on ascertainable physical circumstances.[83]