Altogether, the study of rural work and rents leads to the same conclusion as the analysis of the legal characteristics of villainage. The period from the Conquest onwards may be divided into two stages. In later times, that is from the close of the thirteenth century downwards, the division between the two great classes of tenants and tenements, a contrast strictly legal, is regulated by the material test of the certainty or uncertainty of the service due, and the formal test of the mode of conveyance. In earlier times the classification depends primarily on the economic relation between the manorial centre and the tributary household, labour is deemed servile, rent held to be free. It is only by keeping these two periods clearly distinct, that one is enabled to combine the seemingly conflicting facts in our surveys. If we look at the most ancient of these documents, we shall have to admit that a rent-paying holding is free, nevertheless it would be wrong to infer that when commutation became more or less general, classification was settled in the same way. A servile tenement no longer became free because rent was taken instead of labour; it was still held 'at the will of the lord,' and conveyed by surrender and admittance. When all holdings were fast exchanging labour for rent, the old notions had been surrendered and a new basis for classification found in those legal incidents just mentioned. The development of copyhold belongs to the later period, copyhold being mostly a rent-paying servile tenure. Again, if we turn to the earlier epoch we shall have to remember that the contrast between labour and rent is not to be taken merely as a result of commutation. Local distinctions are fitted on to it in a way which cannot be explained by the mere assumption that every settlement of a rent appeared in the place of an original labour obligation. The contrast is primordial, as one may say, and based on the fact that the labour of a subject appears directly subservient to the wants and arrangements of the superior household, while the payment of rent severs the connexion for a time and leaves each body to move in its own direction till the day when the tributary has to pay again. [Difference in quantity between the impositions of free and unfree population.]