#31. The Combination of Labour.# We now see what great advantages arise from each man learning a single trade thoroughly. This is called the division of labour, because it divides up the work into a great many different operations; nevertheless, it leads men to assist each other, and to work together in manufacturing the same goods. Thus, in producing a book, a great many trades must assist each other: type-founders cast the type; mechanics make the printing press; the paper is manufactured at the paper works; printers' ink is prepared at other works; the publishers arrange the business; the author supplies the copy; the compositors set up the type; the reader corrects the proofs; the pressmen work off the printed sheets; then there are still the bookbinders, and the booksellers, besides a great many other small trades which supply the tools wanted by the principal trades. Thus, society is like a very complicated machine, in which there is a great number of wheels, and wheels within wheels; each part goes on attending to its own business, and doing the same work over and over again. There is what we should call a #complex organization# (Greek, organon, instrument), that is to say, different people and different trades work as instruments of each other, all assisting in the ultimate result. But it is to be observed that nobody plans out these systems of divided labour; indeed few people ever know how many trades there are, and how they are connected together. There are said to be about thirty-six distinct kinds of employment in making and putting together the parts of a piano; there are about forty trades engaged in watchmaking; in the cotton business there are more than a hundred occupations. But new trades are frequently created, especially when any new discovery takes place; thus, there are at least sixteen different trades occupied in photography, or in making the things required by photographers; and railways have produced whole series of employments which did not exist fifty years ago. These trades arise without any Act of Parliament to make them or allow them. There is no law to say how many trades there shall be, nor how many people shall go into each trade, because nobody can tell what will be wanted in future years. These things are arranged by a kind of #social instinct#. Each person takes up the kind of work which seems to suit him and to pay him best at the time.