Classical conditioning is a theory discovered by Pavlov a Russian physiologist he worked on dogs and the digestive system before this study people believed that saliva was produced when food in in the mouth but then Pavlov found out it happened when the dog saw the food, possibly smelling the food. Pavlov used classical conditioning, his experiment was used with a dog. When the bell rings the dog doesn't do anything until after a while Pavlov gives the dog a treat every time the bell is rung so every time the bell rings now the dog will start salivating. This is how systematic desensitisation works, people associate a fear or a phobia by something they may of seen the say that an accident may have occurred causing the phobia e.g. if a man had a car accident and the car that crashed in to him was blue, the man may have a fear of blue now because of this (the dog learning that food comes with the ring of the bell) psychologists can help this by slowly showing the man that blue isn't scary by talking about the colour, seeing the word written on paper then seeing the colour and being comfortable with it, this is then cured of the fear this is called the Hierarchy of fear. This reaction can't be learned so he called this unconditioned response. This theory is what psychologists use to look at phobias, it shows that there is always something too set a behaviour off e.g. if something bad happened in your life and the most thing you remember is a poster on the wall or even a song you listened to that night, you could develop a phobia of that poster or song. The best way to help this is to find the cause and ask the patient to make a list of their worst fear about that phobia.
This is where operant conditioning comes in,