One of the great influences on American philosophy was Charles Sanders Peirce’s pragmaticism. His interest in philosophy began as a hobby but has had wide international repercussion. Pierce’s intellectual career is a lifelong search for a correct account of the nature and function of methods that permit the discovery of truth. The methodology employed for this search was for Peirce a science of sort and therefore he sought in the long history of science valuable lessons for his own project. Surely he must have been aware of the speculation on science by luminaries such as Kant, Hume, Nietzsche, Vico (who called his work The New Science), just to mention a few.

One of his early discoveries was that, despite Descartes’ cogito, scientific intelligences do not begin their activities in and intellectual vacuum. There are presuppositions of science and scientific method and they basically fall into two large classes: religion and common sense. Peirce speculated that scientific activity is based upon religion, whether or not the scientific intelligence is aware of it or not, because the ideals of that method presuppose a search for the truth about a reality not yet known. This idea of faith or basic beliefs being the base of science can be found in both Aquinas Summa and in Thomas Kuhn’s The Structure of Scientific Revolutions. Moreover, Peirce sees knowledge as a means of stabilizing our habitual behavior in response to doubt.

Common sense on the other hand is that set of instinctive beliefs that all normal human beings do not doubt. Peirce speculated that those beliefs were the results of evolutionary change over millennia. Like religion, such original beliefs are not theory and there is a place in his system for theorizing about them, but one should never substituted the theory for the presence and current nature of such beliefs in all humans. That kind of speculation is reminiscent of Wittgenstein’s On Certainty.

According to Peirce, the guiding principle of his “pragmaticism” philosophy is this: if one can define accurately all the conceivable experimental phenomena which the affirmation or denial of a concept could imply, one will have a complete definition of the concept. So this view is principally concerned with establishing the meaning of concepts and beliefs, a philosophical emphasis that would come to dominate the linguistics of the 20th century.

One of the effects of Peirce’s pragmaticism is to distinguish metaphysical propositions that are nonsense from the authentically meaningful propositions of “scientific metaphysics.” The nonsensical propositions are those which have no sense because they do not represent any idea that has observable, sensible effects that can be accorded practical significance.

Scientific metaphysics, for Pierce, is an observational discipline concerning the first and most basic elements of experience; those elements that are so fundamental that they are difficult to discern. Thus scientific metaphysics and science are not part of one continuous discipline—as some of Pierce’s philosophical descendants would later claim—but maintain the traditional hierarchical order of foundational and succeeding disciplines respectively.

Pierce rejects Descartes “paper doubt,” a doubt considered merely as an intellectual exercise, and sidesteps the whole issue of epistemological skepticism. His foundational, scientific metaphysics accordingly begins with phenomenology, the way things are presented to us in experience. He is particularly concerned with the difference between belief and doubt. Real doubt ensues when recalcitrant experience, which is not reflection, causes us to waver in our beliefs. A belief, as Peirce understands it, is not some kind of intellectual disposition to assent to a proposition, but a behavioral habit manifest in action. Therefore, when real doubt ensues it disrupts our usual behavioral patterns. Cartesian doubt, on the other hand, can make no difference to the way we act.

Pierce suggests that knowledge, which he defines as the resolution of disrupted habits by the revision of belief, is a “homeostatic” process. Homeostatis is a concept borrowed from physiology, in which the body employs reaction systems to return to normal functioning in response to environmental upsets. Similarly, Pierce sees knowledge as a means of stabilizing our habitual behavior in response to doubt.

Today Pierce is widely considered the most original and profound of American intellects. He wrote many articles for academic journals but did not publish any work that set out his philosophy. Unfavorable personal circumstances prevented that during his life. But Pierce scholarship has been steadily growing in the last twenty years and his unpublished writing have been appearing in convenient editions for those interested in studying his philosophy. Three such are The Essential Peirce (two volumes, 1992, 1998) and The Cambridge Companion to Peirce.