The quantitative difficulty reduces itself to this. Admitting the greater fertility to-day of those whose occupations are manual, or who have no occupation at all (in other words, of the less select type) and admitting that _at the present moment_ the country is overpopulated, how are we to be certain that we are not within sight of more prosperous times when unemployment will disappear? And how are we to feel assured that the dissemination of knowledge of Birth Control will not, in the long run, lead to a disastrous decline in the birth rate, producing an irretrievable diminution in our numbers? The practical difficulty is here to prophesy what will be the optimum population (i.e., that at which average return of labour per individual would be greatest) for a given country fourteen years ahead――at the time, that is, when the children born to-day would enter the labour market. And here we are in the realm of almost pure guesswork, and probably no economist could be found who would venture upon more than a tentative speculation. What the optimum is at the moment remains even a disputed question. There is reason to suppose that unemployment returns are not necessarily a trustworthy guide to the figure. A consensus of opinion however exists (including that of Mr. Baldwin) that _at the moment_ our numbers are above their optimum, though expectations vary almost infinitely as to what the optimum will be in a few years. Those who hope for a boom in trade are satisfied with the present condition. Others who do not anticipate such an event, would more willingly see an alteration brought about. In the absence of any definite knowledge, the best we can do is not to try to look too far ahead but to consider the solution of our problems as we find them to-day. _At the moment_ the indisputable facts of the problem in this country are that we are over-populated, that contraception is practised too much by the upper and middle classes――perhaps even by the skilled working classes――and not enough by the improvident unskilled masses at the bottom of the social edifice. The outstanding question is whether, as a result of a reduction of our numbers to a point somewhere in the neighbourhood of the economic optimum for this country――by which reduction the existing burden of taxation, an increasing element of which is now devoted to charity and relief, will be correspondingly diminished――our upper and middle classes would be enabled to produce more children, and to continue to produce enough to maintain our numbers in the neighbourhood of their optimum.