4.1 Facts-in-issue

To motivate the use of propositions, we begin with a discussion about facts-in-issue. Facts-in-issue are the relevant facts of a specific case that are contested by each side of a legal dispute. In criminal trials in the UK, the facts-in-issue are the contested facts between the prosecution’s and defence’s version of events, otherwise known as their hypotheses.

There is epistemic uncertainty about the facts-in-issue and so relevant evidence about these issues is presented to the court. The fact finder then considers this evidence to determine the truth of the facts-in-issue, and ultimately the outcome of the case. This means that the language and presentation of facts-in-issue must be precise and accurate. They should allow the fact finder to clearly discriminate between the hypotheses of either side of counsel. The expert scientist must also do so impartially without bias in favour of one side or the other. For scientific evidence, the expert does this by formalising the facts-in-issue into what are known as propositions.