18.18 (i) 'Knowledge' means this knowledge about the acts which ought to be performed. (ii) The 'object of knowledge' is the act which ought to be performed. (iii) 'The knower' is the person who knows that act. The meaning is that the injunction to do acts, like Jyotistoma etc., is a combination of knowledge, object of knowledge, and the knower. Among these, action itself, which is the object of knowledge, is briefly described as threefold - these being the instrument, action and the agent. The instrument forms the materials etc., which are the means. The action consists of the sacrifice etc. The agent is the performer.