자연과학
Objection: "[A] great many things have been explained by matter and motion…." Natural science ("Natural Philosophy" in the text) has made much progress by assuming the existence of matter and mechanical motion. Answer: Scientists ("they who attempt to account of things", the term "scientist" being introduced in the nineteenth century by W. Whewell), do not need to assume that matter and motion exist and that they have effects on an observer's mind. All scientists need to do is to explain why we are affected by certain "ideas" on certain occasions.