A review of the changes in the English elementary and secondary school curricula in Canada from about l900 reveals two kinds of language knowledge: knowing "how" (knowledge measuring aspects of language performance) and knowing "that" (factual information about language). Until approximately l900, the belief existed that knowledge about the principles of language was both necessary for proper speaking and writing and helpful for reading. In short, knowing in the "that" sense was useful in the performance of speaking, writing, and reading, which is knowledge in the "how" sense. This distinction between "knowing about" and "knowing that," although an oversimplification, has been addressed by philosophers and epistemologists. In addition, current language arts instruction is not based on a harmonious consensus about what should be taught and how: progressive approaches include an informational component. Emphasis on knowledge about the principles of language (the "that" sense) existed in Canada until a progressive curriculum, adopted in Alberta in 1937, began a major change as an English-as-use curriculum was introduced. (EL)