 All this suggests a “veil of perception” between us and external objects: we do not have direct unvarnished access to the world, but instead have an access that is mediated by sensory appearances, the character of which might well depend on all kinds of factors (e.g., condition of sense organs, direct brain stimulation, etc.) besides those features of the external world that our perceptual judgments aim to capture. Paraphrasing David Hume (1739: I.2.vi, I.4.ii; 1748: sec 12.1; see also Locke 1690, Berkeley 1710, Russell 1912): nothing is ever directly present to the mind in perception except perceptual appearances.