The magnitude of the value of merchandise would not undergo alteration if the time necessary to produce continued it being same; but this varies whenever the productivity of the work modifies, that is to say, with each alteration that are introduced in the activity of the procedures or of the outer conditions in which the force of the work is pronounced. The productivity then, on the work, depends things among others, of the average ability of the workers, the amplitude and effectiveness of means to produce and exclusively natural circumstances; for example, the same amount of work is represented in a simple porcelain lamp if the conditions have been favorable and in average lamp on the contrary. As a rule, if the productivity of the work increases, diminishing the necessary time for the production of an article, the value of this article falls and reciprocally, if the productivity falls, the value increases. More, whoever they are the variations of its productivity, the same work creates always the same value, working during equal time, only that provides in a certain time a greater or smaller amount of useful values of use or objects, according to which it increases or it diminishes its productivity. Although thanks to an increase of productivity two dresses instead of one take place in the same time, each dress will continue having the same utility that before duplicating the production; but in both dressed two men instead of one can be dressed; therefore, there is increase of material wealth. Nevertheless, the value of the set of useful objects continues being the same: two dresses done in the same time that before in doing one, more are not worth than previously only one. Any modification in the productivity that does the work fecund, increases the amount of articles that work provides and therefore the material wealth, but materially does not modify the value of this increased amount if the total time of work used in its manufacture continues being identical.