The division of labour, which we already saw above as one of the chief forces of history up till now, manifests itself also in the ruling class as the division of mental and material labour, so that inside this class one part appears as the thinkers of the class (its active, conceptive ideologists, who make the perfecting of the illusion of the class about itself their chief source of livelihood), while the others' attitude to these ideas and illusions is more passive and receptive, because they are in reality the active members of this class and have less time to make up illusions and ideas about themselves. Within this class this cleavage can even develop into a certain opposition and hostility between the two parts, which, however, in the case of a practical collision, in which the class itself is endangered, automatically comes to nothing, in which case there also vanishes the semblance that the ruling ideas were not the ideas of the ruling class and had a power distinct from the power of this class. The existence of revolutionary ideas in a particular period presupposes the existence of a revolutionary class; about the premises for the latter sufficient has already been said above.