C.S. Pierce's Pragmatism

Pierce was a great American thinker and his work is hard to summarize. He made great contributions to what is now called Research Methodology and he is best remembered as the man who introduced pragmatism and semiotics (the theory of Signs) to the world. He was also a great mathematician and made discoveries in geophysics.
Pragmatism's maxim: Judge people's ideas by the effects they are supposed to bring.
Faillibilism principle: There are no ultimate truths, only provisional truths until further testing show that there are better ideas.
His theory of Signs gained importance in the XXth century when the emphasis was to understand Languistic and Meanings.
Logic: He identified "Abduction" in addition to well-known "Deduction" and "Induction"

http://en.wikipedia.org/wiki/Charles_Sanders_Pierce#Peirce.27s_philosophy

Peirce's philosophy

It is not sufficiently recognized that Peirce’s career was that of a scientist, not a philosopher; and that during his lifetime he was known and valued chiefly as a scientist, only secondly as a logician, and scarcely at all as a philosopher. Even his work in philosophy and logic will not be understood until this fact becomes a standing premise of Peircian studies. (Max Fisch, in (Moore and Robin 1964, 486).
Peirce was a working scientist for 30 years, and arguably was a professional philosopher only during the five years he lectured at Johns Hopkins. He learned philosophy mainly by reading a few pages of Kant's Critique of Pure Reason in the original German, every day while a Harvard undergraduate. His writings bear on a wide array of disciplines, including astronomy, metrology, geodesy, mathematics, logic, philosophy, the history and philosophy of science, linguistics, economics, and psychology. This work has become the subject of renewed interest and approval, resulting in a revival inspired not only by his anticipations of recent scientific developments but also by his demonstration of how philosophy can be applied effectively to human problems.
Peirce's writings repeatedly refer to a system of three categories, named Firstness, Secondness, and Thirdness, devised early in his career in reaction to his reading of Aristotle, Kant, and Hegel. He later initiated the philosophical tendency known as pragmatism, a variant of which his life-long friend William James made popular. Peirce believed that any truth is provisional, and that the truth of any proposition cannot be certain but only probable. The name he gave to this state of affairs was "fallibilism". This fallibilism and pragmatism may be seen as playing roles in his work similar to those of skepticism and positivism, respectively, in the work of others.
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Pragmatism

Peirce's recipe for pragmatic thinking, going under the label of pragmatism and also known as pragmaticism, is recapitulated in several versions of the so-called pragmatic maxim. Here is one of his more emphatic statements of it:
Pragmaticism was originally enounced in the form of a maxim, as follows: Consider what effects that might conceivably have practical bearings you conceive the objects of your conception to have. Then, your conception of those effects is the whole of your conception of the object. (CP 5.438).
William James, among others, regarded two of Peirce's papers, "The Fixation of Belief" (1877) and "How to Make Our Ideas Clear" (1878) as being the origin of pragmatism. Peirce conceived pragmatism to be a method for clarifying the meaning of difficult ideas through the application of the pragmatic maxim. He differed from William James and the early John Dewey, in some of their tangential enthusiasms, in being decidedly more rationalistic and realistic, in several senses of those terms, throughout the preponderance of his own philosophical moods.
Peirce's pragmatism may be understood as a method of sorting out conceptual confusions by linking the meaning of concepts to their operational or practical consequences. This pragmatism bears no resemblance to "vulgar" pragmatism, which misleadingly connotes a ruthless and Machiavellian search for mercenary or political advantage. Rather, Peirce sought an objectively verifiable method to test the truth of putative knowledge on a way that goes beyond the usual duo of foundational alternatives, namely:
Deduction from self-evident truths, or rationalism;
Induction from experiential phenomena, or empiricism.
His approach is often confused with the latter form of foundationalism, but is distinct from it by virtue of the following three dimensions:
Active process of theory generation, with no prior assurance of truth;
Subsequent application of the contingent theory, aimed toward developing its logical and practical consequences;
Evaluation of the provisional theory's utility for the anticipation of future experience, and that in dual senses of the word: prediction and control. Peirce's appreciation of these three dimensions serves to flesh out a physiognomy of inquiry far more 'solid' than the 'flatter' image of inductive generalization simpliciter, which is merely the relabeling of phenomenological patterns. Peirce's pragmatism was the first time the scientific method was proposed as an epistemology for philosophical questions.
A theory that proves itself more successful in predicting and controlling our world than its rivals is said to be nearer the truth. This is an operational notion of truth employed by scientists. Unlike the other pragmatists, Peirce never explicitly advanced a theory of truth. But his scattered comments about truth have proved influential to several epistemic truth theorists, and as a useful foil for deflationary and correspondence theories of truth.
Pragmatism is regarded as a distinctively American philosophy. As advocated by James, John Dewey, Ferdinand Canning Scott Schiller, George Herbert Mead, and others, it has proved durable and popular. But Peirce did not seize on this fact to enhance his reputation. Instead, what James and others called "pragmatism" so dismayed Peirce that he renamed his own variant pragmaticism, joking that it was "ugly enough to be safe from kidnappers" (CP 5.414).