Legal Abductions

This paper deals with the role of abductive inference in legal reasoning. Both in the determination of the relevant facts and in the determination of their legal consequences abductive inference plays a crucial role, being the first step of such reasoning tasks. Two kinds of legal abduction are distinguished: an explanatory one aiming at the reconstruction of the relevant facts and a classificatory one aiming at a legal conceptualization of those facts. We concentrate on the first kind, stressing the similarities it has with scientific abduction, notably on the concern of truth. We claim that legal abduction is truth-directed, justice being in the first place epistemic justice. 1 Charles S. Peirce and Abduction Charles Sanders Peirce (1839-1914) calls abduction the inference suggesting an explanation. In his early writings instead of abduction he speaks of hypothesis – see e.g. W1: 180, 266 ff. (1865); W1: 362, 430 ff. (1866); W3: 323-338 (1878). At that time his main purpose is to distinguish, in a kantian way, ampliative from non-ampliative inferences. Hypothesis and induction are ampliative inferences while deduction is non-ampliative, being merely explicatory. The point being the difference between ampliative and non-ampliative inferences, in his early writings Peirce does not always draw a clear distinction between hypothesis and induction. Yet he says that induction determines a general character while hypothesis permits the knowledge of causes (W1: 428; cf. e.g. CP 5.272-276, 2.624). Nonetheless, he more often uses hypothesis to denote a classificatory reasoning, depending on a syllogistic scheme, than a causal, explanatory reasoning. But in his later writings he makes a clear threefold distinction between abduction, deduction and induction – see e.g. CP 7.162-255 (1901); CP 5.14-212 (1903). This threefold distinction follows the methodological principles of scientific inquiry according to him. Every scientific inquiry is constituted by three inferential steps: first, by abduction we suggest an hypothesis explaining a fact; second, by deduction we determine the conceivable consequences of the hypothesis; third, by induction we test the conceivable consequences of the hypothesis verifying whether they correspond or not to real consequences1. To sum up for our purposes, hypothesis denotes in Peirce’s early writings a kind of classificatory reasoning, while in his later writings abduction denotes an explanatory reasoning.