Though it is no part of our business here to elaborate the psychology of doubt and belief, it may be well to anticipate a possible criticism on the lines of recent psychological speculation, and to indicate at the outset the practical conception on which the present survey broadly proceeds. To begin with, the conception of freethinking implies that of hindrance, resistance, coercion, difficulty; and as regards objective obstacles the type of all hindrance is restraint upon freedom of speech or publication. In other words, all such restraint is a check upon thinking. On reflection it soon becomes clear that where men dare not say or write what they think, the very power of thinking is at length impaired in the ablest, while the natural stimulus to new thought is withdrawn from the rest. No man can properly develop his mind without contact with other minds, suggestion and criticism being alike factors in every fruitful mental evolution; and though for some the atmosphere of personal intercourse is but slightly necessary to the process of mental construction, even for these the prospect of promulgation is probably essential to the undertaking of the task; and the study of other writers is a condition of useful ratiocination. In any case, it is certain that the exercise of argument is a condition of intellectual growth. Not one man in a million will or can argue closely with himself on issues on which he knows he can say nothing and can never overtly act; and for the average man all reasoning on great problems is a matter of prompting from without. The simple fact that the conversation of uneducated people runs so largely to citation of what "he says" makes clear this dependence. Each brings something to the common store, and progress is set up by "pooling" the mass of small intellectual variations or originalities. Thus in the long run freedom of speech is the measure of a generation's intellectual capacity; [50] and the promoters of such freedom are typically the truest servants of progress.