Truth begins as a social term, referring to a person acting in good faith with respect to another; later it develops into a term indicating good craft, acting appropriately with respect to the material world. Later still it is infused with some abstracted notion of knowledge, some sort of perfect thing. It is at that point that, as Ferrier reminds us, we need a theory not only of knowledge but of ignorance. Ferrier is remembered for the word he coined for theory of knowledge. ‘Epistemology’ has caught on. His word for theory of ignorance has been lost even to the dictionary, although recently it seems to have been easing its way out of the cracks in the internet into a wider consciousness. ‘Agnoiology’ does not really trip off the tongue. Not yet, but perhaps it will. A third element in Ferrier’s philosophy was ‘ontology.’ Was that coined by Kant? Kant’s forebears came from Aberdeen, and Ferrier was writing in St Andrews, so perhaps his notion of theory of existence drifted south via some sort of philosophically inclined current at the Scottish edge of the North Sea.