“All money is a matter of belief.” —Adam Smith
The rate of return, or the level of profit, is one of many issues discussed by Adam Smith in his now famous and influential economics book The Wealth of Nations. Below is a brief excerpt of the first few paragraphs of chapter nine—Of the Profits of Stock. In this chapter Adam Smith lays out his view on profits, returns and interest rates, and also where to look to get some indications and guidance on what level of interest one could reasonably expect. To read the whole chapter, click on the link at the end of the text (emphasis added).
OF THE PROFITS OF STOCK
The rise and fall in the profits of stock depend upon the same causes with the rise and fall in the wages of labour, the increasing or declining state of the wealth of the society; but those causes affect the one and the other very differently.
The increase of stock, which raises wages, tends to lower profit. When the stocks of many rich merchants are turned into the same trade, their mutual competition naturally tends to lower its profit; and when there is a like increase of stock in all the different trades carried on in the same society, the same competition must produce the same effect in them all.*49
It is not easy, it has already been observed, to ascertain what are the average wages of labour even in a particular place, and at a particular time. We can, even in this case, seldom determine more than what are the most usual wages. But even this can seldom be done with regard to the profits of stock. Profit is so very fluctuating, that the person who carries on a particular trade cannot always tell you himself what is the average of his annual profit. It is affected, not only by every variation of price in the commodities which he deals in, but by the good or bad fortune both of his rivals and of his customers, and by a thousand other accidents to which goods when carried either by sea or by land, or even when stored in a warehouse, are liable. It varies, therefore, not only from year to year, but from day to day, and almost from hour to hour. To ascertain what is the average profit of all the different trades carried on in a great kingdom, must be much more difficult; and to judge of what it may have been formerly, or in remote periods of time, with any degree of precision, must be altogether impossible.
But though it may be impossible to determine with any degree of precision, what are or were the average profits of stock, either in the present, or in ancient times, some notion may be formed of them from the interest of money.*50 It may be laid down as a maxim, that wherever a great deal can be made by the use of money, a great deal will commonly be given for the use of it; and that wherever little can be made by it, less will commonly be given for it.*51 According, therefore, as the usual market rate of interest varies in any country, we may be assured that the ordinary profits of stock must vary with it, must sink as it sinks, and rise as it rises. The progress of interest, therefore, may lead us to form some notion of the progress of profit.