The field of “talking” therapy covers a very large, varied and still-developing collection of theories – stretching from 1779 when Franz Mesmer published his theory of animal magnetism, to present day developments in neuroscience, and in between spanning many different areas such as

• theories of the mind, both its conscious and subconscious/unconscious aspects

• theories of motivation, the relationship between thinking and behaviour 

• theories of the influence of the environment and the limits of choice and free will.  

There are many academic workers in the world, busy researching and writing about such ideas.  Some of these theories have led to methods that are used in therapy.  

On the other hand, some therapy methods were developed “in the field”, by therapists trying out new ideas directly on clients, particularly with challenging clients for whom the existing methods weren’t working well. 
In these cases, theories might be considered afterwards, as in “That seemed to work better.. Why did it work better?”and so a theory would be formed. The advantage of this kind of work is that when you’re using a method, you have an organised set of ideas behind it, and sometimes also a basis of some evidence that the method has apparently been shown to be effective, at least some of the time with some people.  However, it’s important to remember when considering evidence, that it’s entirely possible for the theory to be incorrect, because the interpretation of the evidence is faulty.  Academics often disagree with each other, and have competing theories about what evidence may mean.  When a new theory or method first comes out, it’s often the case that the person or persons introducing it are convinced of their theory and are very enthusiastic about it, making broad claims about how many things can be fixed by it.  Then as experience is gathered, the claims are usually  reduced/modified, and one or more of the following is likely to happen

• the modified theory gets included among a large number of other theories in the general accumulation of academic data, as providing a small part of explaining the great complexity of human thinking and behaving

• some enthusiasts will continue offering methods based on the theory as a sole form of therapy, forming a kind of specialised “school” – this is not necessarily a bad thing, provided potential clients are made aware of its limitations, which does not always happen

• a larger number of therapists, and training schools, will include the method along with others, for the trainees to choose from when seeing clients