In the case of alternative demand, that is, where a want may be satisfied by any one of two or more commodities, an increase in the price of one commodity may cause a serious falling off in the demand for that commodity and a substitution of another commodity in its place. Thus a rise in the price of butter causes a decrease in the demand for butter and a corresponding increase in the demand for oleomargarine. Similarly, an increase in the wages of workingmen often results in the substitution of machinery for labor. This bringing in of a less expensive good to take the place of a more expensive one, increasing the demand for the former and diminishing the demand for the latter, is known as the principle of substitution.