Eidola Theatri — Francis Bacon, in Novum Organum, his treatise on the scientific method, identifies four different sources of error, or false idols. Idola tribus, errors caused by human nature, idola specus, errors due to the characteristics of individual humans, idola fori, errors caused by linguistic confusions, and idola theatri (literally “theatrical idols”), errors caused by believing in systems of thought that shape the way we allow ourselves to see reality. Idola can also mean “a spectre” or “a mental image.” Ludlow is using this term to refer directly to his hallucinations at the opera, but is probably also alluding to Bacon’s categories of confusion.