Blake's sanity was called into question as recently as the publication of the 1911 Encyclopædia Britannica, whose entry on Blake comments that "the question whether Blake was or was not mad seems likely to remain in dispute, but there can be no doubt whatever that he was at different periods of his life under the influence of illusions for which there are no outward facts to account, and that much of what he wrote is so far wanting in the quality of sanity as to be without a logical coherence". More @Wikipedia
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