4.3 Competing propositions

When formulating propositions from facts-in-issue, the different sides of an adversarial judicial system form different hypotheses about the events which led to the same factual observation.

For example, as part of a case there might be a DNA sample recovered from a crime scene which was found to match the DNA profile taken from a suspect after their arrest. The prosecution might assert that the defendant was at the location in which the DNA sample was recovered. The defence, on the other hand, might accept that this is the defendant’s DNA but instead assert that it was indirectly transferred there, e.g. from physical contact with another individual who was provably at the crime scene. Both of these hypotheses would reasonably lead to the defendant’s DNA matching the crime scene sample.

Translating these assertions into propositions gives so-called competing propositions. Competing propositions typically come in pairs, one put forward by each side of legal counsel. The standard notation that is used for these propositions is \(H_p\) and \(H_d\) to represent ‘prosecution/defence hypothesis.’