The Behaviourist movement was influential in Philosophy during the 1930's, 40's and 50's with its influence beginning to wane significantly in the 1960's. The Behaviourist movement in Philosophy was motivated in part by answering concerns first raised in Descartes work. And in part by the need to for an account of the mental which would be compatible with materialism and the new scientific world view. While the motivation behind methodological Behaviourism was largely derived from the lack of progress made in the field of Psychology which at that time relied heavily on introspective methods. We have two very different and distinct ways of ascribing mental states and concepts, we can ascribe them on the basis of first person introspection or alternatively we can ascribe them to others on the based on their behaviour. Many philosophers have been deeply suspicious of the ascription of mental states by the means of first person introspection which seems to lead to accepting some kind of Cartesian project.
But according to Behaviourism, the talk of hidden mental events which cannot be observed is totally mistake.The Behaviourist holds that the behavior of an organism is completely exhausted by its observable response to stimuli. The psychology of the said organism simply consists in the relationship between the various stimuli and response. This position was prominent not only in Philosophy but was also widely accepted in psychology with its most notable proponents being B.F Skinner and John B. Watson. For the behaviourist, talk of a hidden mental realm which exists between the stimuli and the response is a fiction. Being in the mental state is no more than the tendency to react to certain stimuli with certain responses. For example, being in pain is no more than a tendency to move away and vocalize the sound 'Ouch' when hit by hard a object with considerable force.
As you can see this simple form of Behaviourism is rather lacking. As behaviour is neither necessary or sufficient for the ascription of a mental state. Take the example of an extraordinary actor who was pretending to be in pain, if the actors acting skills were so refined in that his behaviour was indistinguishable from someone who was actually in pain. This would show that behaviour alone is not necessary for the ascription of a particular mental state. For a brief period of time during the 1940's a plant toxin called Curare was used as anesthetic. In fact Curare does not work as anesthetic but merely causes the total temporary paralysis of a particular subject. A patient being operated on while paralyzed by Curare would be in considerable pain but would not be able to provide any observable evidence indicating their pain. This example shows that behaviour is also not sufficient for the ascription of pain, as it is possible to be in pain without any observational behaviour.
Another problem for Behaviourism as outlined by those like Skinner and Watson, is the distance between certain mental states and the observational behaviour which would confirm that particular mental. Take the belief that Oxford University is the best University in the United Kingdom, what behaviour would verify this. It seems it could be near impossible isolate the correct behaviour for ascribing such a belief.
Philosophers did not have to accept such radical methodological behaviorism, with the majority behaviourist philosophers adopting what is commonly referred to as Logical Behaviourism. Logical Behaviourism is not a theory regarding how experimental psychology should be undertaken it is instead a semantic theory about the meaning of mental terms. According to Logical Behaviourism, the attribution of a mental state to a person or animal simply consists in saying that the person or animal is disposed to behave in a certain way in certain circumstances. For example saying James is thirsty is simply to say that James is disposed to drink water if exposed to an appropriate opportunity to drink some water. This is a considerable improvement over basic behaviourism as it allows the behavioural analysis to open ended or infinite, so it seems we are much better equipped when we are dealing beliefs and other complicated subject matter. We may be able to analyse the belief that Oxford is the best university in the United Kingdom into an opened set of behavioural statements, such as 'Remarking on the reputation of Oxford as a University when asked'. Even if it is not possible in practice to complete such a set of dispositions, the fact that it remains logically possible is enough for maintaining Logical Behaviourism. Logical Behaviourism is also advantageous as it does not require that the abandonment of mental talk as long as we remember that talk of the mental could be replaced by a complete behavioural analysis.
Even with all of this being said in favor of Logical Behaviourism there still seems to be one crucial objection to overcome namely that behaviour is neither necessary or sufficient for the ascription of mental states. But it can be argued that this objection can also be overcome by adopting a richer notion of what constitutes behaviour. The most successful attempt at this was made Hempel in his 1935 paper The Logical Analysis of Psychology. Adopting a verificationist theory of meaning and construing behaviour in the widest possible sense it can be argued that Hempel showed that behaviour is both necessary and sufficient for the ascription of mental states. But whether we are willing to accept Hempel's verification theory of meaning and his wider notion of behaviour which includes every physical fact about a subject is a different matter. For one verificationist theory of meaning have been shown to be hugely problematic and much of what Hempel takes to be Behaviour is deeply debatable. As Hempel seems to be using the word behaviour in way that is contrary to our every day understanding of the term. In fact I believe Hempel's theory has many features in common with some of the identity theories that took the place of Behaviorism in the philosophical community.
A number of other objections have made against Logical Behaviourism. Concerns have made about how Behaviourism fails to provide an account of mental-mental causation. Take the following the example 'Jill's fear of dogs and her belief that a dog is in front of her causes her to run away'. Behaviourism seems to struggle to explain such cases mental-mental causation as it appears that there is no way to explain such cases in terms of explicit behaviour. Again it could be argued that this objection could be avoided by adopting a richer notion of what constitutes behaviour to include facts about the persons physiology. This is related to another objection about the alleged circularity of the behaviourist project, there will be a vast number of appropriate responses to any one stimuli with differing responses being largely down to the differing beliefs of the subject. Therefore it seems there is no way to analyse away the mental without positing beliefs or desires that are not explicitly observable in behaviour.
I'm going to finish off with one final objection (and one bad joke) to behaviourism, it seems that we do not access our own mental states by observing our own behaviour but through first person introspection. This alleged absurdity with behaviourism is often put in the form of a joke.
Two behaviourist psychologists are talking to each after sex, one of them says to the other 'I see can that you enjoyed yourself, but how was it for me'?