The aim of this chapter is to propose a working definition of fiction applicable to the romances written between about 1150 and 1220, making no claim to wider validity. Even so, some assistance will be sought from elsewhere (classical literature, modern philosophical theory) on the grounds that, although some aspects of fiction vary widely over time, others are common to different periods.

To start by taking classical antiquity into brief account is not so irrelevant as it might seem. Plato's criticism of poetry was acceptable to early Christianity at odds with pagan literature and to early medieval thought dominated by Platonism before the relatively late reception of Aristotle, whose Poetics, although available to the Latin West only from the thirteenth century, provided arguments more favourable to fiction than those of Plato.

Plato's criticism rests on the view that the poet is a mere imitator, dealing with appearances rather than with what is real and therefore presenting a lie instead of the truth. The basis of his argument is a radical distinction between poetry and philosophy, later adapted to Christian ends as one between poetry and theology. As Plato's myth of the cave makes clear, the poet resembles the prisoners who, facing backwards, see only the shadows cast by the fire, so that the product of the poet is twice removed from reality.