The Peirceian Influence on Hartshorne’s Subjectivism

by Theodore R. Vitali, C.P

Theodore R. Vitali, C.P., is Assistant Professor of Philosophy at Bellarmine College, Louisville, Kentucky.

The following article appeared in Process Studies, pp. 238-249, Vol. 7, Number 4, Winter, 1977. Process Studies is published quarterly by the Center for Process Studies, 1325 N. College Ave., Claremont, CA 91711. Used by permission. This material was prepared for Religion Online by Ted and Winnie Brock.


The author is concerned with the role Charles Peirce’s categories play in the development of Hartshorne’s principles of internal and external relations. Together with the influence of Whitehead, Peirce’s categories helped shape Hartshorne’s philosophy of subjectivism.


In this paper we shall be principally concerned with investigating the role Peirce’s categories play in the full development of these principles. We will try to show how, together with the influence of Whitehead, they helped to shape in its mature form Hartshorne’s philosophy of subjectivism.

Hartshorne’s philosophy can accurately be described as a philosophy of feeling. If there is anything primordial in Hartshorne’s thought, it is the central place of feeling. The universe -- all reality for that matter -- is a complex of feeling centers. Feeling centers or psychic events plus their correlative term, values, are the root out of which the universe emerges and is. In Creative Synthesis and Philosophic Method Hartshorne brings this out quite clearly. He is concerned in this text with describing H. G. Wells’s vision of reality during the latter’s theistic period. Nevertheless, it is the best description to my knowledge of Hartshorne’s own view of his philosophy of feeling.

Now if the physical as given is essentially feeling, then, since thought can expand, generalize, extrapolate, and abstract, it follows that thought can arrive at no world other than a world of feelings, with their relations, aspects, varieties, and so forth. This is, in one respect, the social view of reality. (CSPM xvii)

From the earliest period of his reflective thought, the period prior to the years at Harvard, Hartshorne had clearly formulated the insight that there was a "unity of feeling between the self and nature as immediately given" (RSP 19). This basic subjectivism would never be lost.

Nevertheless the direction of his thought was along monistic lines. As late as his dissertation in 1923 Hartshorne was grappling with the problem of how to have monistic inclusiveness as the foundation for universal value and truth and still retain feeling centers which would be autonomous of that inclusion (TPP 22-34). An adequate subjectivism had to entail two elements: there had to be feeling centers capable of including objects felt, and there had to be other subjects who were also feeling centers and thus values capable of being included without loss of their own subjectivity. To maintain such a doctrine a clear philosophy of relations had to be formulated, one which contained real internal relations, thus grounding a real sense of inclusion, and also one which contained real external relations, thus establishing a true pluralism of external centers of feeling and value.

The influences of Whitehead and Peirce during the years from 1925 through roughly 1933 help to account for the final clarification and maturation of these principles. As we shall presently see, Whitehead aided Hartshorne in conceiving a truly pluralistic universe through an event-ontology. At the same time Whitehead’s dipolar theism helped safeguard the needed doctrine of inclusion. Peirce, on the other hand, provided suitable categories for expressing Hartshorne’s metaphysics of feeling and also provided the doctrine of the continuum which enabled him to develop a theory of emergent possibilities in contrast to Whitehead’s doctrine of eternal objects.


Whitehead’s philosophy is also a theory of subjectivism. Its "reformed subjectivism" holds subjectivity primary, but it also holds a strong doctrine of objectivity. Objects are given to and not created by the subject. "The many become one and are increased by one" (PR 32). Yet, simple or naive pluralism is not intended. The "many" enter into a novel unity, a new reality. An emergent or creative synthesis, to use Hartshorne’s expression, becomes the "very principle of process and reality." The principle of relativity states: "to be is to be a potential for every (subsequent) becoming" (PR 33). Each item of reality, comments Hartshorne on Whitehead’s principle, is destined to form material for endlessly compounded and recompounded acts of synthesis, producing new and more complex realities (WP 162).

Real relatedness is rooted in this doctrine of prehension. Internal relations are constituted by the feeling or awareness of that which is efficaciously present to it. On the other hand, that which is prehended does not in turn prehend its prehender. The former retains its own objectivity and is only externally related to the actual occasion prehending it. Even in the synthesis by which the "many become one," the "many" remain objectively distinct in themselves. It is the novel occasion, the new "one," which is internally related to that which it prehends and realizes in a new unity.

Memory is the paradigm case of prehension. We prehend and are really related to our past experiences. Yet, the past experiences are not really related to the present memory. The past is not remembered as anticipating the present memory of itself. Relatedness, taken as internal, runs one way only. There is no converse. In short, this is the doctrine of asymmetry so central to Hartshorne and Whitehead in their theories of time, causality, and feeling (WP 11).

The doctrine of prehensions and actual occasions provided Hartshorne with a necessary clarification of inclusion and objective value. Feeling centers are able to include their objects and thus be internally related to them without the loss of the object’s value and freedom. At the same time true creativity could be maintained since the new unity synthesized from the many which were prehended was not merely an aggregate of the many externally related, but something "formally" new.

If this can be asserted about finite centers, what might be said concerning the ultimate center of feeling, God? Sessions clearly points out that during the early period up to and including the dissertation, Hartshorne was troubled by a monistic concept of God which came quite close to the classical concept of Pure Act. Given this absolutist notion with its radical implications for inclusiveness, understood as the source of ultimate value and truth, how could a genuine doctrine of pluralism be held? Sessions tells us that Hartshorne answered in the dissertation with a claim upon divine benevolence flowing from a perfectly good omnipotence (TPP 32). This could hardly do. In fact, such absolutism, whether benevolent or not, argues for a determinism with regard to finite centers of value and freedom. Hartshorne’s pluralism would run the risk of collapsing.

The stress on absolute inclusiveness may well have been a residue of the classical notion of God, at least in terms of the divine omnipotence. It may well have been due, though Hartshorne is not clear on this point, to his awareness of Royce’s concept of inclusiveness found in The World and Individual. In any case, he seems to be caught in a dilemma. How could he maintain a true pluralism while retaining an absolutist concept of God?

W. E. Hocking had suggested to Hartshorne the possibility of dipolar theism. Hocking made some attempts at formulating the possibility of conceiving God both as absolute and relative (contingent), eternal and temporal. Nevertheless, it was Whitehead who had given the most comprehensive and consistent view to date. It was Whitehead’s view, I believe, that brought to finalization Hartshorne’s dipolar theism and thus a way out of the dilemma.

By distinguishing the primordial nature from the consequent state or actuality of God, Whitehead was almost the first, claims Hartshorne, to deal seriously with the divine individuality. While the primoridal nature is absolute, independent, abstract, and neutral with respect to particular determinations, the consequent or relative nature is one in which the divine actuality is conceived as a sequence of determinate, contingent experiences which express both the essence of God and the de facto content of the world God experiences at a given moment. Whereas the divine essence (the primordial nature of God) is absolute impassive, and neutral, the consequent actuality is relative, passive, and value-oriented, with a supreme sensitivity or responsiveness that is "without equivocation, love itself in unadulterated purity" (WP 13).

In terms of internal and external relations, the consequent or relative nature of God is internally related to the world. The world, however, as prehended by God is not in turn internally related to him. It is true that the world has an internal relationship to God in that the world prehends its past and its past is included within the divine consequent nature. In this precise sense the world prehends God. However, in terms of the divine envisagement of the actual world, the relation is asymmetrical. There is no internal relationship, taken in the exact same way, between the world and God, and God and the world. There is a stubborn objectivity to the world in the divine experience. God is passive to the world in the sense that he is dependent upon it for his concrete actuality. If this were not the case then the divine inclusion would mean mutual internal relatedness. The world would lose its independence and identity. The relativity of God in his actual states avoids this difficulty and makes inclusion without monism possible.


There also seems to be a constant theme running through Harts-home’s writings concerning Peirce, especially with regard to his categories and theory of emergent possibilities. The theme is basically an appropriation of the Peirceian theories either in support of his own positions or as providing a more suitable categorical scheme for expressing them. This appropriation is not without adjustment. Nevertheless, the overall impression given is one of general favor, as we shall see.

With regard to the categories and their place in his system, Harts-home relates in The Philosophy and Psychology of Sensation his concept of feeling to the Peirceian categories in terms of the interrationship of feelings: sensations, volitions, and thoughts.

That this union of sense and feeling under the same head is the only scientific one was effectively shown by the analysis of Charles Peirce, who pointed out that the most decisive classifications in science are those based upon mathematical form, and that the common form of sensation and of feelings is given in the fact that both exhibit (relatively) unitary or "simple" qualities (redness, pleasure) whereas willing, or better "striving," is conspicuously dual (an "effort" is always sensed as correlative to "resistance"), and whereas knowing or "meaning" is irreducibly triadic (sign, thing signified, larger mental context or "idea" to or for which it has this signification). (PPS 37)

The categories are presented in this text as reflecting in logical clarity his own doctrine of feeling. In mathematical form they express the doctrine of the interrelatedness of feeling.

This same theme is reiterated in and elaborated on in Beyond Humanism:

Now blueness is not primarily conflict or meaning, but feeling-quality, while "awareness" refers chiefly to meaning, the use of signs. All three categories are "psychic": the "mind" is in all cases a unity of feeling, striving, and meaning. The doctrine of sympathy, which Peirce was one of the first to bold, is that all feeling feels other feeling, all reaction has an object which itself is reactive, and all meaning means other meaning, as well as reactions and feelings. Since the three categories exhaust experience, we could have no other predicates with which to clothe objects; and that we have objects at all is due entirely to the sympathetic duality or imminent sociality of experience. (BH 185)

Recalling Hartshorne’s description of the social view of reality, the categories are able to be seen as the adequate categorial scheme of reality because the mind can only "expand, generalize, extrapolate, and abstract" that which is given in feelings. They "exhaust experience." Thus, they have metaphysical universality since no experience can be instanced which would not be a monad, dyad, or triad.

The phrase "all reactions have as an object that which is itself reactive" is not, strictly speaking, Peirce’s doctrine. Hartshorne modified the notion of the monad or first as a simple independence, claiming instead that it was itself a reactive agent in one context and an independent entity in another. We shall consider this modification in greater detail later.

In any case, Hartshorne claims that "Peirce’s definition of feeling, reaction and meaning in terms of the monad, dyad and the triad, is one of the few great achievements of its kind" (BH 285). In Reality as Social Process, he attests that the Peirceian categories reaffirm his own beliefs that feelings and their relationships constitute the essence of reality (RSP 20).

Finally, an overall assessment of the categories is made in Creative Synthesis.

Values may be considered under three heads: acting rightly, thinking correctly, and experiencing satisfyingly. In other words, goodness, truth and beauty. But as Peirce held, the order is wrong. The basic value is the intrinsic value of experiencing, as a unity of feeling inclusive of whatever volition and thought the experience contains, and exhibiting harmony or beauty. . . . Thinking, Peirce held, is one form of acting, and hence logic as a normative science is a branch of ethics. Both presuppose aesthetics, in a generalized sense; the study of what makes experiences good in themselves. (CSPM 303)

The categories are not explicitly mentioned, though they are implied. All logic is reduced to ethics and ethics to aesthetics. All meaning, therefore, is a relationship of feelings to feelings. This entails that all meaning, ethical and logical, is ultimately intelligible only through the relationship of feelings. These latter find their ultimate meaning through the categories. Therefore the metaphysics of feeling, the heart and soul of Hartshorne’s philosophy, is contained and expressed in the categories formulated by Peirce.

Hartshorne goes so far as to claim that his "neoclassicism, surrelativism and creativism . . . can be viewed as Peirceian" if the "categories are purified of certain ambiguities" and if the "one-sided emphasis upon continuity (his synechism)" which he thinks "inconsistent or confused, is corrected" (CSPM xvi).

The complete appropriation of the Peirceian categories as a vehicle for expressing his metaphysics of feeling depends on the purification of "certain ambiguities" in the categories, principally "Firstness" and the removal of the inconsistencies in Peirce’s synechism. The problem of the categories and the problem of synechism are mutually relevant. The correction of the former leads to the correction of the latter.

Hartshorne’s problem stems from Peirce’s definition of the monad as a simple quality of feeling (CP 6:198). The monad is a kind of feeling abstractable from any particular instance. Peirce defined the monad or first more precisely as "the absence of reaction -- of feeling another." In sensing a specific quality, such as magenta, we imagine that all the rest of our consciousness -- memory, thought, everything except this "feeling of magenta -- is utterly wiped out, and with that is erased all possibility of comparing the magenta with anything else or of estimating it as more or less bright. That is what you must think the pure sense-quality to be" (CP 6:198).

If the first is conceived in this way, Hartshorne responds, it appears at best to be "nothing but a limiting concept, a vacuous case which no actual experience could quite realize." The first would be the same as abstractness, possibility or essence. No actual feeling with its actual quality could be a first. Firstness would thus have to be conceived in total independence of concrete and definite actuality. It would be mere potentiality (SPCP 459).

Instead of such an understanding of Firstness, Hartshorne insists that an actual feeling is always a second. This may be assumed if an actual feeling is always conceived in terms of its relationship to a stimulus, that is, to a prior first. The question might arise, however, if such an assumption were made, whether it would follow that the "stimulating entity is in its turn related to the feeling it elicits." In other words, would this entail direct symmetry? Hartshorne thinks not. The stimulus as event need not be taken as relative to the subsequent feeling. Rather, the "feeling is second to the thing felt, which in this context is first; and this relation is not reversible or symmetrical." There is an actual first and an actual second. The first event to which the second is relative, may in another context be itself a second to prior firsts.

Hartshorne is prompt to admit that in fact Peirce had implied this, though he (Peirce) had failed to develop it adequately. Hartshorne probably had in mind the text in which Peirce states: "If state A is affected by state B, and state B by state C, then A is affected by state C, though not so much so. It follows that if A is affectible by B, B is not affectible by A" (CF 6:129). Hartshorne’s own position reflects this quite clearly: "The Firstness or Absoluteness is, to be sure, relative only, but for all that, perfectly definite and genuine. The earlier experience was strictly independent of its successor, but not of its predecessor (SPCP 459).

Even admitting a doctrine of asymmetry, Peirce’s category of Firstness, taken as simple independence, and his use of vision as his model, made it "impossible for him to conceive a definite unit of experience having definite predecessors and successors, to the former of which it could be second or relative, and to the latter first or absolute." As Peirce conceived it, "no definite Firstness or Secondness can be found in a syncretistic conceived process" (SPCP 460). Without definiteness, neither asymmetry nor a developed logic of internal and external relations would be possible.

Looked at more closely, the problem concerns the continuum. Peirce conceived the continuum as consisting of both actualities and possibilities. Between any set of feelings there exists an infinite number of actualities. Between feelings x and y there is an infinite number of z’s. Upon seeing one color pass into another, an infinite number of shades must be passed through. The time interval is said by Peirce to be infinitesimal (CP 6:131).

Given an infinite number of actualities between x and y, no definite value can be assigned to either x or y because no clear delineation of terms is possible. The terms x and y would have an infinity of intermediate values between them. Neither the relative absoluteness of firsts, nor the internal relatedness of seconds could be maintained. Neither asymmetry nor internal and external relations could be sustained. A form of Zeno’s paradoxes would apply.

Hartshorne’s criticism is clearly stated in Creative Synthesis:

That continuity belongs with the abstract, indefinite, possible, infinite, not with the concrete, actual, finite, is the truth missed by Bergson, Peirce and Dewey, but seen by James and Whitehead. . . .It seems to be the real bearing of the Zeno paradoxes. A continuum either has no parts, or indefinite or infinite but merely possible parts; definite multiple actuality must be discrete, and, at least for any finite portion of space-time, finite in its actual constituents. Peirce saw that possibilities form continua, thus all possible hues, shades and tints of red. But it seems obvious that the actual array of colors does not present all of these: there are always gaps. . . . It could not be otherwise. Actuality as such implies arbitrary breaking of a continuum. . . . Peirce’s bias towards continuity, which made him blur the distinction between discrete actuality and continuous possibility in favor of a belief in actually continuous becoming and motion, was responsible. It led him to his extraordinary doctrine that a human experience has neither finite or zero but infinitesimal duration so that in a single second, say, we have an infinite number of successive experiences, each drawing inferences from the previous, and thus we are always infinitely far from identifying a definite experience with definite unmediated data. (CSPM 122f)

Hartshorne’s criticism and correction rest upon the distinction between actuality and potentiality The relatively nonrelative, the first, in a sense is abstract because the predecessor of an event can only be conceived by way of an abstraction. To know the past, for example, as the "content of memory we must abstract from the novelties introduced by the remembering experience. Yesterday as known today is today minus all that is new about today." The relatively nonrelative or absolute is thus relatively abstract. Furthermore, the relatively absolute is a potential for future experiences. Yesterday was no mere possibility. It was a possibility in a relative sense since it furnished that possibility for a certain kind of successor which would not have been otherwise possible. Yet, it remains only abstract with reference to its successors. Actuality adds definiteness to potentiality. Today adds definiteness to the kind of today which yesterday made possible (SPCP 460).

On the basis of this distinction a continuum of possibilities can be had without the risk of Zeno’s paradoxes becoming applicable to it. The definiteness of terms is established through the actuality of seconds while the continuum of firsts is a continuum of abstract possibility.

On the basis of what we have just examined, we can conclude that at least two significant elements were derived from Peirce: the categories and the doctrine of the continuum with its emergent possibilities. Once corrected of their inconsistencies and confusions, they became suitable for Hartshorne’s metaphysics of feeling. The Whiteheadian doctrine of prehension enabled him to criticize Peirce’s category of Firstness and thus make it suitable for the more important doctrine of the emergence of possibility in the continuum. Whitehead’s role is obviously important because it aided Hartshorne in adapting the categories and the continuum to meet the needs of his own system. Both Peirce and Whitehead thus contributed to the clarification of internal and external relations which grounded Hartshorne’s subjectivism and facilitated his metaphysics of experience.


While admitting the enormous role played by Whitehead in refining the Peirceian categories and the doctrine of the continuum, it was the Peirceian vision which ultimately dominated in the construction of Hartshorne’s metaphysics. This can be seen if we examine Hartshorne’s departure from Whitehead on the matter of realistic essences. Hartshorne shifts to a temporalistic interpretation of emergent possibility radically transforming the atemporal view which the doctrine of eternal objects suggests.

The key to understanding this fundamental shift lies in the distinction between potentiality and actuality, i.e. between generality and definiteness. Hartshorne follows Peirce in identifying possibility and generality, while definiteness or determinateness is found in actuality. These terms appear synonymous for both Peirce and Hartshorne, but Whitehead distinguishes definiteness from determinateness (PR 38). Eternal objects are defined as "forms of definiteness" (PR 32). They confer on actual occasions that formal unity which enters into the identity of the actual occasion. The determination of the actual occasion, the complete actual identity in all its detail, results from both definiteness and position. Definiteness is "the illustration of select eternal objects," and position is "relative status in a nexus of actual entities" (PR 38) Actuality or definiteness is thus constituted by both definiteness and position. Definiteness appears on the side of the eternal objects and thus on the side of potentiality. For full actuality position must be present as well as definiteness.

Hartshorne’s position eliminates this distinction between definiteness and determinateness. Potentiality and generality go together. Definiteness can only be on the side of actuality. In an important paper written on the subject of realistic essences in Santayana, Hartshorne gives perhaps his most detailed arguments against the definiteness-determinateness of essences qua potentials.

If essences are determinate and complete apart from existence, then all relations of essence to existence, or by virtue of existence, are external to essence. Its relations to existence are purely contingent. But can the determined receive a relation, even contingently? What relevance could the relation possibly have? It could make no difference to the essence that it has the existential relation. In short, "it" would not have it. Existence would thus be like the Thomist’s God, who is said not to be related to the world . . . although the world is related to Him. (Santayana 171)

The language in this text is classical. Existence and actuality are here identified. Normally they are distinguished (discussion of the ontological argument rests upon this distinction). The context indicates, however, that Hartshorne intends by existence concrete actuality.

With this in mind, the gist of Hartshorne’s objection is that qua potentialities, the definite essences leave nothing for actuality to confer upon them in terms of further determination. If actuality were to add anything, what would it be? If the addition were internal to the essence, then they would no longer be what they were. In this sense, definiteness would not be a valid designation for the essences because definiteness in fact would be due to the actualization of the potential. If only an external relationship were conferred, actualization would have absolutely no significance for the essence itself. Actuality would add nothing, and concreteness would lose any significant meaning. Existence or actuality would thus be "formally empty."

In Hartshorne’s view of creative synthesis actuality is far from "formally empty." In terms of the Peirceian categories, secondness confers something upon firsts which the latter could not provide for insofar as they are firsts or potentials, namely, their formal determination and significance (causal) in a new actual entity. That which was merely determinable now is made determinate by the formalizing process of the second in its act of synthesis. The firsts acquire new meaning and definiteness as causally efficacious in the new unity, a definiteness they did not possess as potentials for the becoming of a subsequent event (CDLC 62-66). Hartshorne provides an example:

Let us take an example of choice. I may choose to try to be kind rather than injurious to a person who has injured me. But the actual word or deed must be more definite than anything such choice can envisage prior to action. Choice is among "intrinsically general alternatives," although what is done is never general in the same degree. This is the meaning of choice: it is determining which determinable to particularize through further determinations not yet in being. (Santayana 172)

On these terms, definiteness cannot be attached to potentiality without either destroying the formal unity of the essences or the import of actuality in conferring something significant upon essences. The chain of firsts would not be increased through seconds, since seconds would add nothing real or significant to the antecedent chain. Potentialities would be eternally and definitively fixed. To avoid this difficulty, one which would vitiate his entire system, Hartshorne denies any such definiteness in essences and identifies instead definiteness with determinateness on the side of actuality, with universality and determinability being conceived on the side of potentiality. Hartshorne boldly asserts in Creative Synthesis that the ultimate principle of definiteness is "the principle of experiencing as partly free or self-creative, and this principle being ultimate, accounts for definiteness without the help of any other principles" (CSPM 62).

Hartshorne’s view can best be summarized as a temporal view of possibility. In the act of creative synthesis only two factors are involved: the past as the data providing for a determinable future and the actual experience which, in causing its own formal unity and concrete actuality, gives definiteness and determination to its own potentiality. White-head’s view requires a third factor, the novel form supplied by the initial aim. Peirce’s position does not and thus coincides with Hartshorne s. Their views depend on the identification of determinability and universality, determination and actuality. In my judgment, the general metaphysical foundation for Hartshorne’s philosophy is exactly this temporal view of possibility and actuality, generality and concreteness. It is precisely the relations, internal and external, between seconds and firsts elaborated on and systematized by Peirce, though transformed by Hartshorne, which provide the foundation for Hartshorne’s metaphysics.


Hartshorne’s thesis, derived from Peirce, that determination renders specific that which is only general and universal, poses some difficulties when examined from a Whiteheadian perspective. The actual occasion creates its own determinateness from a determinable but indefinite past through its act of creative synthesis, but its formal principle of unity, its initial aim or principle of purpose according to which the occasion chooses its self-determination, that by and for which the synthesis occurs, is not given. It appears to come from the occasion itself, but its act of self-realization already presupposes it. It cannot come from the past, for that past by definition is indefinite as to the final form of its unity. Hartshorne’s temporal view of possibility excludes any other alternatives.

Whitehead’s own account, which seems to assign the exact degree of relevance of every eternal object to each and every temporal situation by means of the primordial valuation of God (PR 46, 64, 248) has its own problems, for then the specification of the initial aims occurs without recourse to God’s temporal, responsive experience. Lewis S. Ford seems to have resolved this issue by retaining a formal principle of unification, namely, a doctrine of eternal objects in the primordial nature of God constituting pure possibility without sacrificing Hartshorne’s insights concerning the temporal emergence of real possibility, namely, a doctrine of emergent real possibility due both to logical possibility and to position, the latter established by the emergence of the past actual world in the consequent nature (TPP 58-65).

Although Whitehead’s analysis of prehension and his dipolar theism enabled Hartshorne to construct a consistent theory of internal and external relations, Peirce provided the major categorial scheme which Hartshorne finally adopted. As corrected by recourse to Whiteheadian principles, it provided the basic structure for Hartshorne’s temporal view of process, which allowed for the emergence of possibility without requiring any eternally definite essences.

It may be, however, that further modification of Hartshorne’s Peirceianism is in order to resolve the difficulties surrounding the actuality’s formal principle of unity. It would seem that it is through Whitehead that the Peirceian character of Hartshorne’s philosophy can be brought to full fruition.



BH -- Charles Hartshorne, Beyond Humanism: Essays in the New Philosophy of Nature. Bison Book Edition, Lincoln: University of Nebraska Press, 1968.

CDLC -- Charles Hartshorne, "Creativity and the Deductive Logic of Causality," Review of Metaphysics, 2811 (Sept., 1973), 62-75.

CP -- Charles Peirce, Collected Papers of Charles Sanders Peirce. Charles Hartshorne and Paul Weiss, eds. Volume 6. Cambridge: Harvard University Press, 1935.

CSPM -- Charles Hartshorne, Creative Synthesis and Philosophic Method. LaSalle: Open Court Publishing Co., 1971.

PPS -- Charles Hartshorne, The Philosophy and Psychology of Sensation. Port Washington: Kennikat Press, 1964.

RSP -- Charles Hartshorne, Reality as Social Process: Studies in Metaphysics and Religion. New York: Hafner Publishing Co., 1971.

Santayana -- Charles Hartshorne, "Santayana’s Doctrine of Essences," pp. 135-85 in The Philosophy of George Santayana, Paul Arthur Schillp, ed. New York: Tudor Publishing Co., 1951.

SPCP -- Charles Hartshorne, "Charles Sanders Peirce’s One Contribution to Philosophy and His Most Serious Mistake," pp. 445-74 in Studies in the Philosophy of Charles Sanders Peirce. Second Series, Edward G. Moore and Richard S. Robin, eds. Amherst: University of Massachusetts Press, 1964.

TPP -- Lewis S. Ford, "Whitehead’s Differences from Hartshorne, pp. 58-83; and William Lad Sessions, "Hartshorne’s Early Philosophy," pp. 10-34 in Two Process Philosophers. Lewis S. Ford, ed. Tallahassee: American Academy of Religion, 1973.

WP -- Charles Hartshorne, Whitehead’s Philosophy. Lincoln: University of Nebraska Press, 1972.