A Treatise of Human Nature taste to be in the other), arguing that unextended perceptions must somehow exist without having a location. But the contrary problem arises for dualists: how can extended perceptions (of extended objects) possibly be conjoined to a simple substance? Indeed, Hume waggishly adds, this is basically the same problem that theologians commonly press against Spinoza's naturalistic metaphysics: thus if the theologians manage to solve the problem of extended perceptions belonging to a simple substance, then they give "that famous atheist" Spinoza a solution to the problem of extended objects as modes of a simple substance. Finally, Hume examines "causal relations", arguing
Chemistry: A Volatile History of a flame – this led Cavendish to name the gas inflammable air, which he believed to be one and the same as phlogiston. Cavendish, though he did not realise it, made an important observation about burning phlogiston in air; a dewy liquid was formed on the inside of the glassware: water. This should have had enormous repercussions for the whole scientific community in the 1700s, who still believed water to be an elemental substance. Yet, if water could be "made" by burning inflammable air, then water is "not" an element, but a compound. However, it simply did not occur