Hume argues in defence of equality throughout his political writings, often by pointing to "nature". My main objective is to reconcile the conception of nature presupposed in those arguments with his theory of the artificial foundation of society. In my opinion, nature is understood from what may be called a developmental point of view when Hume alludes to it in discussing equality. To make this clear, I explore the significance of labour in Hume's idea of society, particularly in connection with his account of exchange and commerce. Thus it is shown that the principal function of exchange is the coordination of labour, through which human beings' power of mind and body develops, and they become "serviceable to each other, as by nature they are fitted to be." Encouragement of labour through exchange requires equality, and thus it is an indispensable condition for human beings' natural potentiality to be properly actualised.