Whilst behaviourism seems at home dealing with certain types of behaviour – such as pain and happiness – the more private the experience the more difficult it is to account for it in behavioural terms. For instance, it is common to talk about “having a picture in my mind” or seeing something “in the mind’s eye”. However, since behaviourism must account for these in terms of the physical, there exists a problem.

One solution proposed by Ryle is that when we “see” things in our minds what we are really doing is pretending to actually see them. So, when I imagine a picture of a dog, I am pretending as if I am actually seeing a dog (though, obviously, I know that I am pretending).

Greater problems exist for logical behaviourism when we think of the different types of behaviour that a situation might produce. For instance, two people can watch the same film and react in opposite ways: one might hate it, the other one love it. If we say that their reactions differ because of other complex factors (of upbringing, personality, etc.), then the behaviourist can still argue that their responses are a response to stimuli – although complex stimuli - and not an example of some private, non-accessible “mind” at work. However, if we cannot predict how someone will react in a certain situation, then how can we be certain that they are just responding to stimuli and not actually thinking and choosing with a private Cartesian self?

Another problem, related to the last one, is the clarity of the concepts of response and stimulus. For instance, if it is possible to react in any number of ways to a certain stimulus – such as the film in the above example – then we can argue that the response is too various to suggest a definite one-to-one relationship between the stimulus and the response. Also, to turn things around, we might think of situations where a number of different types of stimulus produce the same response. For instance, you may answer the phone in any number of ways – abruptly, cheerfully, reluctantly, expectantly – depending on how you feel, what time it is, etc. If, as these problems seem to suggest, neither stimuls or response can be clearly defined, it leaves the dualist or non-behaviourist an opening to say, “Mightn’t there be some other reason for people to act in a certain way? What about a conscious thinking entity called a “mind”?