According to this middle ground, there is something essentially potentially public about mental states though the behavioural expression must be described in mental terms if it is to ground the ascription of mental states. Nevertheless, on this third account, testimony is necessary to bridge the gap between having or being in a mental state and reporting or expressing it (whether verbally or by behavioural expression) to others.
In any case, whatever view of the metaphysics of mind one takes, however closely mental states and behaviour are conceptually tied together, much of what determines diagnosis is not just a matter of patients’ occurrent mental states but information about when they began, what prompted them, what their significance and meaning is for the patient.
In psychiatric practice direct assessment of a patient is often supplemented with collateral history from other informants. This is particularly important in elderly patients who have dementia. Because of their dementia a patient may not recall certain crucial symptoms. For example a patient with dementia may develop persecutory delusions at night only and try and leave the house or repeatedly phone the police and be distressed. This may not occur every night so a direct assessment of these symptoms may not be practical. When assessed in the clinic during daytime, however, the patient might have no recollection these symptoms. Clinical judgement has to rely on a relative’s account of events to formulate diagnosis and a treatment plan. To gather this information requires testimony.
Why does testimony not fit the internalist model of justification of the traditional model of knowledge? The problem, in a nutshell, is that an individual cannot do enough to vouch for the status of knowledge transferred. For this to be possible, testimony would have to be justified in terms of, perhaps by being reduced to, processes which do fit an internalist analysis. But this is not possible.
Suppose, for example, that internalist accounts could be given of perception and induction (neither of which seems plausible). An internalist account of testimony would then be possible providing that testimony could be reduced to a combination of perception (of others, of their utterances, etc.) together with inductions from their previous reliability, for example. David Hume attempted to outline just such a defence of testimony in his Enquiries Concerning Human Understanding [Hume 1975: 109-116]. But as the contemporary philosophy Tony Coady convincingly argues, no such attempt can work [Coady 1992: 79-100]. We will mention just two of Coady’s criticisms of Hume which suggest the principled difficulty of any such attempt.
The first objection is that Hume’s defence depends on establishing inductive correlations between past instances of testimony and the truth of beliefs successfully communicated. But there is, in fact, much less evidence available to individuals than Hume supposes. Summarising Coady, Peter Lipton puts the point thus:
Hume’s discussion systematically hides the fact that our evidential base is far too slender to underwrite in this way even a small fraction of the testimony we rightly accept. Perhaps the main device Hume uses here is to appeal to the correlations we have observed to obtain between various types of testimony and the facts. This appeal to communal observation closes a vicious circle, since you can only in general know what others have observed on the basis of their testimony. The only evidence that you can legitimately appeal to consists of correlations between what you yourself have heard and what you yourself have seen, and this provides far less evidence than would be required to support inductively the wide range and variety of generalisations that would cover all the unchecked testimony you actually accept. [Lipton 1998: 15]
A second line of objection is that the observations that an individual might make are not themselves free from past testimony and thus cannot be used to justify it independently. The quickest argument for this is that observations are framed in language and language is taught through testimony. (One might argue that observation statements are linguistic and thus depend on the teaching of language by testimony. Equally, one might argue that the process