Establishing the truth is one of the aims of the legal process. The search for the truth is taken up by the judge who, in order to arrive at a decision, has to decide, among the allegations of the parts involved, which are true and which are false, distinguishing the narratives that refer to existing facts from those that only assert putative facts. The judge fulfills the epistemological role which law must also face up to. Hence the importance of taking account of the evidence as the basis for justifying the decision as well as understanding the underlying types of reasoning required for this activity. The judge must not be a victim of a naive realism. He must be aware that most of the time he is making use of inductions and therefore his conclusions, albeit based on true premises, are never necessary, characterizing only one possible response. It is of the utmost importance to recognize the need for explicit justification of the decisions taken. Decisions require arguments capable of persuading the parts involved, as well as anyone who is interested in the process, of its acceptability.