My text comes from a text-book:

My theme is that this is nonsense, both in the United States and in Great Britain. Or, to be more precise, that it over-simplifies the reasons why the insanity defence excuses. To make my point clear, however, I must begin by distinguishing different sorts and purposes of explanation where human behaviour is concerned.

Explanations

Explanations of human behaviour are used in at least five ways:

1. to predict future behaviour (for example in psychiatric or political prognoses);

2. to produce future behaviour (for example in elections or psychiatric treatment);

3. to prevent future behaviour (for example in child-rearing);

4. to satisfy curiosity about past behaviour (for example in history);

5. to decide whether past or current behaviour is morally or legally excusable.

This paper is concerned only with explanations of the kind which are relevant to (5); it is not about all kinds of explanation. In particular it is concerned with the sorts which seem to be offered to criminal courts when excusing or mitigating actions. At the sentencing stage psychiatrists in court – and especially in British courts – are often expected also to testify about the treatability of defendants or make prognoses about them; but that sort of testimony is outside the scope of this paper.