Conditioning forms the basis of all behavioural psychology, and is a simple explanation for how people and animals learn to do things. There are two types of conditioning - classical and operant - and several extensions to the basic theory, the most common of which is social learning theory. The seminal behavioural psychologists were Pavlov, Thorndike, Skinner, Watson, and Bandura. This area of psychology is very determinist and completely rejects the possibility that people and animals have any form of cognitive processing ability or even free will.
All organisms have innate reflex responses to stimuli in the environment around them, for example the presence of food will make a dog drool - it cannot choose not to drool as it is a biological response. Ivan Pavlov noticed that the dogs in his house would start drooling at the sound of the footsteps of the person that came to feed them, and before there was any food present. He reasoned that the dogs had learned (through association) that the footsteps signified food - it is important to remember that the dogs did not realise this through deduction or any reasoning process, but by pure involuntary association of two environmental stimuli.
In this example the innate stimulus (food) is called an unconditioned stimulus, the new stimulus before it is learned (footsteps) is called a neutral stimulus NS, the new stimulus after it is learned is called a conditioned stimulus CS, the response to the original innate stimulus (drooling in the presence of food) is called an unconditioned response UCR, and the response to the newly learned stimulus (drooling at the sound of footsteps) is called a conditioned response CR.
Pavlov went on to conduct further experiments on the dogs using bells and tuning forks as stimuli.
The essential idea of classical conditioning is therefore that learning is the result of pairing a novel stimulus with an already present or innate one, and that when the novel stimulus is encountered in the future it will always lead to the same response. The organism has no control over this, and so its behaviour is said to be environmentally determined. But surely this is too simplistic to provide an explanation for all types of learning?
The basic principle behind operant conditioning is that if an animal or person acts on the environment in some way, and they are then rewarded in some way then they will do it again. If, however, there is no reward then they are unlikely to repeat the action; and if they receive a punishment then they are most likely to avoid repeating the action.
An example might be to do with eating. If an organism picks and eats a red berry from a bush (the action) and it tastes sweet (the reward) then they will pick another and another and so on. If the berry tasted bitter (punishment) then they would avoid picking and eating another. If the berry were tasteless and was of no benefit to the organism then they are unlikely to pick and eat another.
Another word for reward is reinforcement. Reinforcement can be positive and negative. A positive reinforcement is one in which a behaviour is followed by a stimulus that is seen as pleasant in some way. A negative reinforcement is one in which a behaviour removes an unpleasant stimulus (e.g. putting on a jumper when it is cold).
Punishment is the consequence of a behaviour (e.g. eating a bitter tasting berry) that makes the behaviour less to occur again. Punishment can be positive by introducing an unpleasant consequence, or negative by removing a pleasant state (e.g. opening a window in winter removes the warmth from a room).
Extinction is when a behaviour dies out because it stops being reinforced, however through spontaneous recovery it can quickly be restored if the reinforcement reappears.
Operant conditioning can be used to shape behaviour - in other words to encourage the repetition of a desirable behaviour through reinforcement, and stamp out an undesirable behaviour by lack of reinforcement or even punishment. An example of this might be for a parent to praise a child who does his/her homework on the day it is set, but to be indifferent to a child who leaves it to the last minute.