The mental factors (caitasika) are the nature and activities of the mind

The operation of the consciousness and mental factors (caittas) is closely connected with a person's character, temperament, disposition, and wisdom. If you wish to understand how the mental factors operate, you can observe each person's facial expressions, gaze, countenance, speech, behavior, and speed of reaction from the moment they first encounter a matter until they finally make a decision. From this, you can discern the process and speed of each mental factor's operation, as well as how heavy each person's habitual tendencies are and how strong their power of wisdom is. This whole series of mental activities is both a manifestation of a person's disposition, habitual tendencies, afflictions, and wisdom, and also a manifestation of the mental factors.

Some people are hot-tempered and rather coarse of mind. After coming into contact with people and affairs, they only make a rough discernment, ignoring right or wrong and the details, and assume that what they have discerned is ultimate and infallible. Then feelings arise—joy, anger, greed, or aversion—with very heavy grasping, and without further ado they directly make a choice. The operation of their mental factors is simple and fast, but the consequences may be unthinkable. Others, after a rough discernment and once feelings have arisen, will again carefully discern and analyze, then correct their mistaken understanding; their feelings change, and only then do they make a decision. The operation of their mental factors is somewhat more complex and will run repeatedly. Many people, as their discernment deepens continually, undergo constant changes in the mental factor of feeling; they are swayed by people, things, and events, their minds completely immersed therein, unable to transcend.

A rational person, if they have not thoroughly understood people, things, and affairs, will not develop any thoughts or emotions, nor will they easily make judgments or choices; they do not take their temporary, rough understanding to be ultimate, but will observe, discriminate, and deliberate over and over again. A person of cultivation, even when what they discern is something they like or dislike, remains unmoved in mind, transcendent above things, and liberated.

For careless people, the mental factors operate quickly and simply; for those of meticulous mind, the mental factors operate slowly, deeply, and complexly. For those with heavy afflictions, the mental factors also operate complexly, entangled and unresolved. For the dull-witted, perhaps after a quick discernment they find their ability insufficient and give up, and the mental factors quickly cease; or perhaps they want to discern clearly, and then the mental factors operate extremely slowly—long discernment, long feeling, long deliberation (manana)—yet they simply cannot make a final decision. The intelligent and wise may discern clearly in a flash, deeply knowing its import; or they may discern it thoroughly in great depth and detail, without error.

The operation of the mental factors is extremely intricate and complex, closely related to the weight of each person's character, temperament, disposition, afflictions, and attachments, and also closely related to each person's cultivation, practice, meditative concentration (samādhi), precepts, and wisdom.