BG Chap 18 - Factors that motivate and constitute action
Knowledge, the object of knowledge, and the knower are the three factors that motivate action. The senses (instruments), the work (object) and the doer (subject) are the three constituents of action. Any work done by any human being has these elements. Before one acts, there is some impetus, which is called inspiration. Any solution arrived at before work is actualized, is a subtle form of work. Then work takes the form of action. The same principles which operate in scriptures dealing with knowledge (jñana-kāṇḍa) also operate in the scriptures dealing with action (karma-kāṇḍa). The process of knowledge means to do acts with the understanding that one is different from the body (jñana). The object of knowledge (jñeyaṁ) is ātmā. The shelter of such knowledge is the jñānī. These three aspects of knowledge are related to action, and thus Kṛṣṇa explains them in terms of action and grammatical cases.
Corresponding to the process of knowing (jñana) is the instrument of action or the process of action, since the meaning of jñana is that by which something is known. It is the instrumental case in grammar which indicates an instrument (knowledge) by which the subject (knower) achieves an action. What is to be known (jñeyam) – ātmā - corresponds to what is to be done. This is the accusative case in grammar which expresses the object of an action (ātmā). He who is the knower of the action is the subject and corresponds to the agent of action. This is the nominative case in grammar which expresses the subject of the verb. The rule for an action has three constituents – the instrument, the object and the subject. For example ‘I (subject) realize the ātmā (object) thru jñana’ (instrument). Or ‘I (subject) perform jyotiṣṭoma sacrifice (object) by oblations’ (instrument). The process of knowledge, the object of knowledge and the knower act as a base for performance of niṣkāma-karma.