  This is a convenient place at which to introduce the last of the nine substances, the ‘mind’ (manas). It is defined by The Manual of Reason (TS18) as a sixth sense-faculty, one by which a person ‘perceives’ their inner mental objects (beliefs, pleasure sensations etc.) In other words, it is a faculty of introspection. Naturally, we need an argument why this faculty cannot be identified as belonging to the self, and the usual Nyāya claim is that the self is the agent of cognising, while the mind is an instrument for cognising, just as we must distinguish between the axe-man, who is the agent chopping the tree, and the axe, which is the instrument for chopping. The Nyāya also claim that the mind has another function, which is to ‘switch’ between the different sense-faculties, it being assumed that, while we are being subjected to sense-impressions from different faculties simultaneously, we only attend to one at a time.