These principles of reason or common sense are often called by other names, such as _intuitions_, _intuitive truths_, _first principles_, etc. Thus all the powers of mind are arranged in the four general classes, viz., _the intellect_, _the susceptibilities_, _the will_, and _reason_ or _common sense_. In regard to the power of mind called _reason_, what is claimed here is, not that either the common people or metaphysicians have usually thus clearly set forth what is here so described and named; but that all men, learned and unlearned, allow that there are truths which are necessarily believed by all mankind; that these are the foundation of all _reasoning_, and that they _often_ are called _reason_. So when any one is found to lack a belief in certain of these intuitive truths, he is said to have “lost his reason.” And when any act or assertion is seen to contradict any of these truths, it is said to be “contrary to reason.” Therefore it is proper to put the belief in these implanted truths as a distinct power of the mind, and to call it “the reason.” And as the belief of these truths is _common_ to all men, it is also proper to call it _common sense_. CHAPTER XIII. NATURE OF MIND.—REGULATION OF THE THOUGHTS. A system of natural religion includes not only the existence and natural attributes of the Creator, but his moral character and the duties owed to Him, to our fellow‐beings and to ourselves. To discover these by the principles of common sense, unaided by revelation, we must again turn to our own minds as our only directory. This demands a more enlarged consideration of many of the specific powers and operations of mind, as developed by experience and observation. Mode of regulating our thoughts. The mode by which the succession of our thoughts is regulated is intimately connected with several subjects to be discussed, and will, therefore, first receive attention. It will be found that our _sensations_ and _perceptions_ vary in vividness and distinctness according to the strength and permanency of certain feelings of _desire_ which coexist with them. For example, we are continually hearing a multitude of sounds, but in respect to many of them, as we feel no desire to know the cause or nature of them, these sensations are so feeble and indistinct as scarcely ever to be recalled to the mind or recognized by any act of memory; but should we hear some strange wailing sound, immediately the desire would arise to ascertain its nature and cause. It would immediately become an object of distinct and vivid perception, and continue so as long as the desire lasted.