The Oxford Dictionary of Philosophy defines it as: Generally any simple and memorable rule or guide for living; for example, 'neither a borrower nor a lender be'.
In Kantian ethics, the categorical imperative provides a test on maxims for determining whether the actions they refer to are right, wrong, or permissible.
The categorical imperative is stated canonically as: "Act only according to that maxim whereby you can, at the same time, will that it should become a universal law.
It might appear to someone that he has acted entirely "from duty", but this could always be an illusion of self-interest: of wanting to see oneself in the best, most noble light.
Michael Polanyi in his account of tacit knowledge stressed the importance of the maxim in focusing both explicit and implicit modes of understanding.