Those eight rules contain all the logic that I think proper to use in my reasoning; and perhaps even they weren’t much needed: the logic they contain might have been supplied by the natural workings of our understanding. Our Aristotelian intellectuals and logicians don’t exhibit so much superiority over ordinary folk in their reason and ability that I want to imitate them by delivering a long system of rules and precepts to direct our judgment in philosophy! All the rules of this sort are very easy to discover, but extremely difficult to apply; and even empirical science, which seems the most natural and simple of all, requires the utmost stretch of human judgment. Every phenomenon in Nature is compounded and modified in so many details that in order to arrive at the decisive point we must carefully separate whatever is superfluous and investigate through new experiments whether every detail of the first experiment was essential to it. These new experiments are open to critical examination of the same kind; so that we need the utmost constancy to persevere in our enquiry, and the utmost skill to choose the right way among so many that present themselves. If this is the case even in •physical science, how much more in •the sciences of human nature, where there is a much greater complication of details, and where the beliefs and feelings that are essential to any action of the mind are so unconscious and obscure that they often escape our strictest attention, and are not only unaccountable in their causes but not even known to exist! I greatly fear that the small success I meet with in my enquiries will make this remark sound like an apology rather than—·what it really is·—a boast! If anything can give me confidence that I am proceeding on the right lines, it will be the widening of my range of empirical data as much as possible; so it may be proper at this point to examine the reasoning faculty of nonhuman animals as well as that of human creatures.