Sections III and IV are ostensibly a series of illustrations of the rule stated at the end of II. But these illustrations, especially one to which he devotes §IV, are tied to philosophical issues that have been addressed independently.

The first illustration (hardness) is the one closest to the idea of “operational definitions,” that concepts might be defined by operations used to test their application. That idea is due to a physicist, Percy Bridgman (1882–1961), and I don’t know of a place where Bridgman speaks of Peirce or pragmatism; but Bridgman spent his whole academic life at Harvard and was already a young man when William James, who also taught at Harvard, drew broad attention to pragmatism and when Peirce was still publicly presenting his ideas. Thinking about operationism (the advocacy of operational definitions) is a good way of thinking about the implications of Peirce’s rule. But be sure to note also Peirce’s comments about meaning and “modes of speech” and facts and “arrangements of facts.”

Peirce’s discussion of force also has ties to a labeled philosophical position. “Instrumentalism” is the view that theoretical concepts in science serve not to refer to an underlying reality but instead serve as tools, “instruments,” for organizing our knowledge of phenomena, of observed “effects.”

But it is Peirce’s discussion of the concept of reality in §IV that is the view most closely attached to him, and it have received considerable attention as a position that might be held without commitment to pragmatism generally. And, since it is closely tied to views of truth, which we will see to be tied to questions of meaning, it is important for us in that regard also. As you think about Peirce’s conception of reality, think back to what he says about the example of the diamond, which he mentions again on p. 301 and which is often mentioned in discussing his ideas of reality. (It’s worth noting that Peirce later moderated what he wanted to say about cases like these, but it’s what he say here that makes clearest the special contribution of pragmatism to thinking about meaning.)