 So it is not so much the production of data that makes Hume’s method experimental rather than his way of “processing” the data gathered in various forms of experiments. This method can be reconstructed as a version of analysis and synthesis inspired by Newton’s Opticks (see  section 4.8  below), that begins with phenomena from the historical and everyday observation of human behavior, and its analysis proceeds by such “experiments … judiciously collected and compar’d” (THN I.10), in order to arrive at analogies among various instances “from the observation of several parallel instances” (EHU 8.13). The products of comparative analysis so conducted are the principles of various faculties, like perception, imagination, reason, etc., whose interaction results in ideas and impressions causing behaviour, but their contribution can hardly be measured and the principles of their interaction can hardly be quantified—not even in principle (see also Hume’s anti-mathematicism discussed in  section 4.7).  So their relations cannot be represented in an algebraic way, in terms of relations of quantities, so they cannot be mathematized either. Instead, they remain qualitatively different principles of human nature, and the explanation of human phenomena consists in a description of how these principles with their distinctive characteristics figure in producing them.