To understand human psychology, we have to first understand how the mind operates.  The mind is classified into different categories based on function. Here we consider the functions of manas (mind), citta (the part of the mind that we are not conscious of) and buddhi (intelligence; the decision making or active part of the mind that interfaces between the manas and citta).

All information from the senses is conveyed to the manas. To make sense of this information, the buddhi scans the citta which is the memory storage. Information in this memory storage is organized into five categories, corresponding to the five senses.

The buddhi scans the citta, and performs ‘pattern matching’ – it matches the sensory input into the manas with the stored information in the citta. When there is a match, the buddhi registers it.

As an example, consider that a person observes ice-cream.

1. The sense of sight conveys the sensation of the ice-cream into the manas. At this stage, the information is only a sensation.
2. The buddhi scans the citta, matches the sensation with stored memory that contains the necessary information to recognize ice-cream. This information includes the word ‘ice-cream’, memory of the taste, whether or not ice-cream was found desirable in the past, etc.

The registering of sensations into the manas is the process of pratyakṣa lit. ‘before one’s eyes’. Comparison of the information with already known information, and inferring something about the object is the process of anumāna.

The citta is the storehouse of all our past memories, not just from this life, but also from unlimited past lives. We only recollect what is in this life. Memories are stored according to the intensity of emotions that accompany the memories. Emotions are memory records of past experiences.

The term saṁskāra is used for memories and corresponding emotions stored in the citta. For example, if we ate ice-cream in the past and really enjoyed it, then that memory is stored deeper into our citta than other saṁskāras. Seeing ice-cream in the present triggers the stored saṁskāra, and if the saṁskāra is really strong, that is, the memory of the experience or emotion to taste it is strong (also called rāga (liking)), the intelligence processes the memory and converts it into desire or decisive thought to eat the ice-cream. This thought is conveyed as a sensation into the manas, which conveys the information to the senses, and the senses than act to acquire the ice-cream.

This means that all actions are preceded by thoughts that are preceded by feelings (i.e. memories of prior experience). First there is feeling, then the feeling gets converted into thought, and this is followed by action. Feelings are of two types: rāga (like) and dveṣa (dislike). Ultimately they originate from the beginningless identification a person has with the body (asmitā), which originates in avidyā (see here for more information).

Human psychology, then, is very simple to understand. From avidyā originate saṁskāras of rāga and dveṣa, which are converted by the buddhi into thoughts, and onward to the senses through the manas resulting in actions. In this way, the ātman which identifies with the body is run by its saṁskāras.  It may be worthwhile to note that the stimuli for recall of emotion need not be from the external senses – they may also be generated by the buddhi itself, as happens in dreams.

To summarize, the manas registers a sensation, the buddhi interfaces with the citta to interpret the sensation. The process of interpretation also results in recall of emotion associated with the sensation. This recalled emotion is converted by the intelligence into thought of possessing or rejecting the object. The thought is passed onto the manas, and then to the senses resulting in action.