And without transgressing the limits which the theory of Marx imposes on us, such a further fact is very easy to find. Adam Smith opens his _Wealth of Nations_ with a discussion of it. The chief cause, he says, which in all progressive countries increases the productive power of the individual labourer, is not the development among a few of potentialities which are above the average, but a more effective development of potentialities common to all, in consequence of labour being divided, so that each man devotes his life to the doing of some one thing. Thus if ten ordinary men were to engage in the business of pin-making, each making every part of every pin for himself, each man would probably complete but one pin in a day. But if each man makes one part, and nothing else but that, thus repeating incessantly a single series of motions, each will acquire the knack of working with such rapidity that the ten together will make daily, not ten pins, but some thousands. Here we have labour divided by its different applications, but not requiring different degrees of capacity. We have the average labour of the average man still. And here we have a fact which, unlike the fact of skill--a thing in its nature confined to the few only--affords a real explanation, up to a certain point, of how ordinary labour as a whole, without ceasing to be ordinary labour, may rise from a lower to a higher grade of efficiency. But such simple divisions of labour as those which are here in question fail, for a reason which will be specified in another moment, to carry us far in the history of industrial progress. They do but bring us to the starting-point of production as it exists to-day. The efficiency of productive effort has made all its most astounding advances since the precise time at which the _Wealth of Nations_ was written; and these advances we shall find that it is quite impossible to explain merely by a further division of average and equal labour. Such a further division has no doubt been an element of the process; but it is an explanation which itself requires explaining. Even in Adam Smith's time two other factors were at work, which have ever since been growing in magnitude and importance; and the secret of modern production lies, we shall find, in these. I call them two, but fundamentally there is only one, for that which is most obvious, and of which I shall speak first, is explainable only as the direct result of the second. This, the most obvious factor, is the modern development of machinery. The other is the growing application of exceptional mental powers, not to the _manual labour of the men by whom these powers are possessed_, but to the _process of directing and co-ordinating the divided labours of others_.