The frequency and impressiveness with which different classes of relations are repeated in conscious experience, thus primarily determining the succession in which they are generalized, there result certain derivative principles to which this succession must more immediately and obviously conform. First in importance comes _the directness with which personal welfare is affected_. While, among surrounding things, many do not appreciably influence the body in any way, some act detrimentally and some beneficially, in various degrees; and manifestly, those things whose actions on the organism are most influential, will, cæteris paribus, be those whose laws of action are earliest observed. Second in order, is _the conspicuousness of one or both the phenomena between which a relation is to be perceived_. On every side are countless phenomena so concealed as to be detected only by close observation; others not obtrusive enough to attract notice; others which moderately solicit the attention; others so imposing or vivid as to force themselves upon consciousness; and supposing incidental conditions to be the same, these last will of course be among the first to have their relations generalized. In the third place, we have _the absolute frequency with which the relations occur_. There are coexistences and sequences of all degrees of commonness, from those which are ever present to those which are extremely rare; and it is clear that the rare coexistences and sequences, as well as the sequences which are very long in taking place, will not be reduced to law so soon as those which are familiar and rapid. Fourthly has to be added _the relative frequency of occurrence_. Many events and appearances are more or less limited to times and places; and as a relation which does not exist within the environment of an observer, cannot be cognized by him, however common it may be elsewhere or in another age, we have to take account of the surrounding physical circumstances, as well as the state of society, of the arts, and of the sciences—all of which affect the frequency with which certain groups of facts are exposed to observation. The fifth corollary to be noticed, is, that the succession in which different classes of phenomena are reduced to law, depends in part on their _simplicity_. Phenomena presenting great composition of causes or conditions, have their essential relations so masked, that it requires accumulated experiences to impress upon consciousness the true connexion of antecedents and consequents they involve. Hence, other things equal, the progress of generalization will be from the simple to the complex; and this it is which M. Comte has wrongly asserted to be the sole regulative principle of the progress. Sixth, and last, comes _the degree of abstractness_. Concrete relations are the earliest acquisitions. The colligation of any group of these into a general relation, which is the first step in abstraction,