The five skandhas are a way to divide up the processes of what makes up a sentient being in Buddhist philosophy, such as a human. The Sanskrit term skandha means "heap" or "pile", as the five groups consist a number of separate elements, and can get very large, if analysed in a serious way.
The Buddha taught that the universe and the beings in it are made out of six elements. Earth (solidity), wind (motility, or energy), fire (heat), water (fluidity), space (the lack of obstruction, see akasha), and consciousness. The first five are classed as being 'material', or rupa, the last being ‘mental’, or citta.
So why are beings not just described as consisting of a mind and a body? The answer to that is that when a being is divided into the portions described by the skandha model, the processes of existence and experience become a little clearer. It is worth noting that there are other ways of dividing up beings conceptually, such as the 18 dhatus etc.
The skandhas are listed in a specific order, as follows, moving from the most 'coarse' to the least.
- Form (rupa)
- Perception (vedana)
- Sensation (samjna)
- Volitions (samskara), and
- Consciousness (vijnana).
To take these in order:
- Form originally meant the physical body of a being. Later on in the development of Mahayana Buddhist philosophy, it actually came to mean all the physical objects a being is aware of, and not just their body. This is something that changed as the way of looking at reality became less objective, and the subjective experience of a being was analysed on a closer level, and the concept that our subjective experience is a kind of 'universe' took hold with the advent of the Idealist school, called Yogachara (or sometimes Cittamatra or Vijnanavada)
What is always included in this skandha are the beings physical sense organs - the eyes, ears, nose, tongue and organs of touch (such as the skin).
- The second, perception, is the subjective experience of a sense object, such as the smell of a rose. It also contains an element of distinguishing and recognition. Here a being perceives and focuses on a particular sensory object. The object is differentiated from other things, such as a patch of red in a certain shape is seen as being different to a nearby patch of green. This kind of experience is devoid of higher-level conceptualisation, and is not yet thought of as being good, bad, or whatever. It's the basic sensory input into a sentient being.
- The third, sensation, is where conceptualisation starts. This is a very basic response of either pain, pleasure or indifference to the sensory input. The basics of an emotional response to the sense object. Most are not responded to with indifference, but rather they either produce at least a very small emotional response of pleasure or displeasure.
- The fourth, volition, is a 'grab-bag' of mental factors. One of these is the mental factor of karma, that is to say, the conditioned mental habits that have been built up over a being's lifetimes. The factor of volition will encompass the desire the being has to move away, ignore or move towards (either physically or mentally) a sense object. It is anything that is not included in the other four skandhas that contributes to and makes up our experience.
- The fifth, consciousness, relates to the six sense consciousnesses human beings have (other beings may have more or less than six). In Buddhist terminology, consciousness (vijnana) is simply 'clear awareness'. It is the simple, direct, subjective experience of something. It cannot exist without something to be aware of, so it is fair to say consciousness must always be conscious of something.
Rather than have one 'consciousness', Buddhism teaches that we have one consciousness for each of our senses. So you have eye, ear, nose, tongue, skin and mind consciousness. The last may seem a little odd, but makes sense if you think about it further. You have thoughts and emotions, and are aware of them. Because of this, they are like another form of sense object, although they are mental objects, not physical ones. A being is only aware of one of the sense consciousnesses at any one time, and the mind rapidly flicks from one to another, building up a model of what's occurring.
The system of the five skandhas makes more sense when an example is used.
Picture a woman going for a walk. As she walks past a lawn that has had the grass freshly cut, her nose is affected by the chemicals released from the cut grass. This, so far, relates to her form.
The smell of the grass is perceived, and focussed on as being a sense object - in this case a smell of something. This is perception.
The experience, based on the conditioning of past experiences is judged to be 'pleasant', and she breathes deeper. She thinks back to when her dad used to cut the grass at home, and the way she used to like the smell of it, years ago. This is the functioning of both sensation and volition. Due to her reaction to it, new conditioned responses have been laid down in her mind - which if backed by any kind of intention to act on the sensation, produces karma.
Throughout this, the sensations have all been related to smell, so the sense-consciousness of smell was the one that was perceiving the experience. This is the consciousness skandha.
The most important teaching of all of this is that here is no permanent, unchanging element that makes up a being. Sentient beings arise from causes and conditions, and do not have an eternal Self - they are Empty. The full realisation of this stops the rounds of Samsaric rebirths, since the being realises that there is nothing to hold onto as 'me', just impermanent mental and physical processes.