In a commentary on clinical judgement for Advances in Psychiatric Treatment, I've made a quick aside on the myth of the given which the editor, reasonably, would like explaining. But given that anything more than a sentence or so will distract from the main business, how quickly can one summarise Sellar’s key argument against it? Here is a first stab.
... Such judgement falls prey to the criticism made by the philosopher Wilfrid Sellars of what he called the ‘myth of the given’ (Sellars 1997). Sellars’ target was the idea that empirical knowledge could be given a sure foundation in direct perceptual reports independent of any uncertain background theory. But, he argued, such reports would need not only to be reliable indicators of whatever features they concerned, but also to be known to be reliable. Otherwise they would no more be reports, or judgements, about anything than the reliable squawk of a parrot. That necessary extra knowledge however undermines the hope that perceptual reports can be an independent foundation for empirical knowledge.