In Query 23, which Newton added to the Latin translation of the Opticks, he declared that investigations in natural philosophy should follow the mathematical methods of analysis, to discover principles and propositions, and synthesis, to demonstrate new propositions. He has proposed a method of reasoning and knowledge. In the next sentence, however, he states that analysis allows us to proceed from “compositions to ingredients,” which appears to be chymists’ method of decomposing material things. This study confirms that Newton did indeed follow mathematicians’ concept of analysis and synthesis in his optical investigations. Through analysis he discovered principles or propositions—for example, that sunlight consists of rays of different colors—while the synthesis demonstrated new propositions, such as the formation of the rainbow and not that white light is composed of rays of different colors. With the exception of this single query, Newton never used the terms “analysis” and “synthesis” in his optical writings. Only in the second half of the eighteenth century, beginning with the French, were these terms applied to the decomposition and recombination of rays of light. The second part of this paper traces this transition to the modern usage of the terms “analysis” and “synthesis.”