An association between two events. Made famous by Pavlov's dogs,  classical conditioning is the process whereby two events become so closely associated that one always predicts the other.   Pavlov demonstrated that by ringing a bell when ever he fed his dogs,  eventually the bell itself was sufficient to cause the physical reaction of 'drooling'  that was previously only caused be the presence of food.  It is this process of classical conditioning which allows us to use a clicker to mark the behaviour we wish to train in our dogs. 

Charging a clicker.  By repeatedly following random clicks with a treat or reward of some sort,  the click itself takes on the characteristics of the reward and is therefore able to reinforce the dog's behaviour.  This charging process is only necessary once for each dog,  but is essential to carry out before clicker training commences.

A temporary association. Typically classical conditioning may be temporary.  That is to say if the two events are not associated with one another for a while,  then the association between them breaks down and the training effect is lost.  For this reason,  we always follow the click with a reward as soon as possible.  However a small gap in time between the two does not seem to diminish the power of the click,  and it is this very useful phenomenon, which allows us to click and strengthen behaviour even when we cannot reach our dog.   The reward can be given after we have relocated.  Provided the time elapsed is small,  and/or we do not break the association too often,  the clicker will maintain its power.

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