As well as developing four rules to guide his reason, Descartes also devises a four-maxim moral code to guide his behavior while he undergoes his period of skeptical doubt. This ensures that he will not have to remain indecisive in his actions while he willfully becomes indecisive in his judgments.

The first maxim is to remain faithful to the laws and customs of his country and his religion. He acknowledges that this choice is somewhat arbitrary given that he has undertaken to abandon all his former opinions and prejudices. However, he notes that if he is to get on in his own country while he dismantles his former opinions he would do well to let his actions be guided by customs of his own country rather than those of some foreign nation. Noting that there is often a difference between what people say and think and what they do, Descartes resolves to follow only the actions of those in his country who are considered most sensible. In cases of conflicting opinions as to how one ought to behave, he always opts for the most moderate option so that he is least likely to err drastically. In particular, he resolves not to allow himself to be bound to promises that would restrict his freedom to alter his judgment later.

His second maxim is to remain firm and decisive in his actions. Even a wrong decision is better than indecision, since indecision takes one nowhere. If there is no obviously true and certain decision to be made, Descartes opts for the most probably right decision, and treats that decision as if it were true and certain. Not only will this save him from never acting (since certainty is hard to find) but it will also save him from any future regrets he would experience if he were less decisive.

His third maxim is to try to master himself and not external factors, to work to change his desires rather than the world. We cannot control external events with any certainty, so we are bound to meet with disappointment if we allow our happiness to be governed by external factors. Ideally, we come to see our thoughts as the one thing we have control over, and to recognize that if even with our best efforts we cannot change something in the world, then that thing is, for all intents and purposes, impossible to change. It takes a great deal of work and meditation to achieve such mastery of the mind, but it brings greater peace and happiness than any worldly success.

His fourth maxim is to find the best possible occupation in life. He concludes that following the present method of philosophy is the best he can do. For one thing, he has found great satisfaction with it, and for another, his only motive for adopting these moral maxims is so that he can pursue this method further. Through this method, he hopes to find certainty and happiness.

Having made up his mind on these maxims, Descartes heads out into the world and spends the next nine years traveling, conversing with others, and further developing his mathematical studies. He remains detached from the business of the world, acting as a spectator, carefully uprooting all the errors or unjustified opinions in his mind and taking careful note of any experiences that he might be able to build upon. Finally, in 1629, he settles in Holland, away from people he knows, where he manages to enjoy the solitude necessary for careful study as well as all the amenities of city life.