Another example from chemistry:I have deduced all the explanations from a simple principle, that pure or vital air is composed of a principle particular to it, which forms its base, and which I have named the oxygen principle, combined with the matter of fire and heat. Once this principle was admitted, the main difficulties of chemistry appeared to dissipate and vanish, and all the phenomena were explained with an astonishing simplicity.According to the accepted phlogiston theory, burning objects give off the substance phlogiston, whereas, according to Lavoisier, burning objects combine with oxygen. The main point of Lavoisier’s argument is that his theory can explain the fact that bodies undergoing combustion increase in weight rather than decrease. To explain the same fact, proponents of the phlogiston theory had to make such odd assumptions as that the phlogiston that was supposedly given off had ”negative weight.”