This essay takes a transhistorical leap to connect the philosophy of Thomas Reid to the dramatic presentation of ethical choices in Shakespeare's Macbeth. Juxtaposing the two figures reveals an underlying moral ontology common to both. This shared ontology is remarkably nuanced, ultimately affirming moral liberty whilst decisively registering the fallibility of the ‘moral faculty.’ The final section asks whether the degree of comparability warrants any further speculation, revisiting the question of a ‘common humanity.’.