It can be interesting for students to investigate what words the dictionary cannot really define. Obvious examples are the words that denote colour: all the dictionary can do is give examples, like the sky, a ripe lemon, blood, or grass.
Others are elemental nouns like sleep, fire, or verbs like see or know: these are words that lively dons and tutors sometimes introduce at university interviews and ask for definitions, to invite a reaction.
The word know and its abstract, knowledge, have caused trouble down the ages, Plato having drawn attention to their problems in his Theatetus and Sophist—and raising questions also in Meno.
Epistemology in the English-speaking world developed in the 17th century, and then began what Professor Gilbert Ryle (1900-76) called the tug-of-war between empiricists and rationalists—which went on and on.
It was not until the twentieth century, when the English-speaking philosophers began to use linguistic analysis, that the unproductive nature of this dispute became apparent. Knowledge is an ancient and generic word, instituted in the time of man’s innocency to embrace what is a convoluted nexus of sense data, acceptance, extrapolation, vocabulary, desire, memory, experience, conjecture, calculation and logic.
Knowledge includes both the empirical and the rational: and Gilbert Ryle concludes his entry on Epistemology in The Concise Encyclopaedia of Philosophy and Philosophers* by saying that as far as rationalists and empiricists are concerned, ‘Their tug-of-war lacks a rope.’
Epistemology, in the 21st century, is seemingly going to be an area where philosophy, psychology and neuroscience intertwine.