Whitehead's epistemology is primarily empiricism. In fact, Whitehead says that experience is "infallible": "What you have experienced you have experienced" (6). But, there is much interpretation involved in experience. Whitehead believes experience to be derived of three different modes. Two of these modes combine into one final mode, termed "symbolic reference". His work Symbolism is to describe symbolic reference. He says, "It is the thesis of this work that human symbolism has its origin in the symbolic interplay between two distinct modes of direct perception of the external world" (30).
The Kantian element of Whitehead can be seen in his epistemology. While the nature of the world can be construed in many analytical ways, Whitehead believes that we know nothing but the empirical world and his metaphysical ultimates.
Any interpretation of sense-experience must arise from the present and from the empirical world. In this way, history must presuppose a metaphysic. However, it does not seem that Whitehead is entirely an empiricist, though that is where the brunt of his epistemological stance lies. For example, because an occasion is related to the world, to God and to the forms, it has access, in a sense, to these forms or eternal objects/receptacle, which are given by God and sorted for relevance to the occasion in question.
To get an adequate account of "human mentality" means several things must be examined. First, how one can know correctly. Secondly, how one can be wrong, and lastly how we distinguish truth from error (7). Whitehead believes there is a type of "mental functioning" that automatically reveals knowledge of a fact. Another type of mental functioning relies on this indubitable functioning and is fallible. This type of functioning is "only trustworthy by reason of its satisfaction of certain criteria provided by the first type of functioning" (7). Whitehead calls the first type "Direct Recognition" and the second type "Symbolic Reference" (7).
Whitehead defines symbolism in terms of how the brain is functioning. He writes, "The human mind is functioning symbolically when some components of its experience elicit consciousness, beliefs, emotions, and usages, respecting other components of its experience. The former set of components are the `symbols', and the latter set constitute the `meaning' of symbols" (7-8). Direct experience elicits some type of response by the organism and the organism uses the symbols (objects, words, etc) from the initial direct experience to apply to other areas of its experience. He terms this transition of symbol to meaning "Symbolic Reference" (8). Symbolic reference requires a relationship between the symbol and meaning. It cannot be arbitrary. It requires common ground that "cannot be expressed without reference to the perfected percipient" and the active synthetic activity of the occasion in question (9). While the relationship between symbol and meaning cannot be arbitrary, there are also no such things as natural symbols - symbols that would function as natural, universal symbols. "There are no components of experience which are symbols or only meanings" (10). This symbolic reference is a kind of two-way street for Whitehead. For example, in using language, symbols are used in a kind of double fashion: "from things to words on the part of the speaker, and from words back to things on the part of the listener" (12).
Experience, for Whitehead, is not something passive. It is active; it is something that is done by the occasion. Symbolic Reference is something that must be done by an active agent. There must be an "active synthetic element" (8). This active synthetic element, or activity of an occasion arises because of the nature of the occasion. Since an actual occasion is an always becoming, concrescing event, the activity of an occasion in perception is, in a sense, self-creating (9). This active synthetic part played by the occasion is reminiscent of Kant and the categories. For Kant, the categories play an active role in how we experience the world. There is something similar in Whitehead. He writes, ". . . the colour and the spatial perspective are abstract elements, characterizing the concrete way in which the wall enters into our experience" (15). It is an abstraction that makes the object appear as an `other.' The fundamental, ontological relationship is already in the experience. One occasion or group of occasion experiences another group of occasions and abstracts extension and color from the other set. But the reality is that this other set is simply another group of occasions, perishing and becoming as the first group is perishing and becoming. For one society to perceive another society in this way means that the perceiving society must deny or "discard" the fundamental relationship between both societies or occasions (15-16). In the sense that all occasions are connected by this relationship, nothing happens independently of anything else. However, because of this type of perception and abstraction, it seems that things really are independent of one another. "In this sense", Whitehead writes, "contemporary events happen independently" (16). He terms this mode of experience "Presentational Immediacy" (16). Presentational immediacy expresses how "things" are related to one another and at the same time, seem to preserve a mutual independence" (16).
Whitehead listed three main facts about presentational immediacy. First, he said that ". . . the sense-data involved depend on the percipient organism and its spatial relations to the perceived organisms" (23). Secondly, the world one sees appears to be extended and full of "things". Lastly he said that presentational immediacy is only present in higher level organisms (23). So, this image of extension always accompanies presentational immediacy. They are bound together. The reality of extension and spatial things is only appearance. Whitehead writes, "In this appearance the world discloses itself to be a community of actual things, which are actual in the same sense as we are" (21). The medium through which this happens is what are generally termed "qualities". These qualities may or may not be a part of the actual world as they can "with equal truth be described as our sensations or as the qualities of the actual things which we perceive" (21-22). Qualities themselves are "relational between the perceiving subject and the perceived things" (22). One must abstract qualities from subjects themselves. Extension is the "scheme of the morphology of the complex organisms forming the community of the contemporary world" (22). All of this means that "sense-data . . . introduce[s] the extended physical entities into our experience under perspectives provided by this spatial scheme" (22).
Presentational immediacy is something that is somewhat controllable by the person. At one moment in time a person experiences all kinds of emotions, feelings etc., that pick and choose such things to focus on. Differing emotions at various times affect the way one perceives things by presentational immediacy. There is a difference between the "thing" existing in its own right and the way it is perceived by presentational immediacy. Whitehead says, " . . . presentational immediacy is the peculiar way in which contemporary things are `objectively' in our experience, and that among the abstract entities which constitute factors in the mode of introduction are those abstractions usually called sense-data . . ." (25). This objectification in presentational immediacy argues against the idea of a Cartesian world. The very objectification is an "abstraction" (25). This abstraction is "nature's mode of interaction " (26). The abstraction that is done means that the thought is conforming itself to nature. The abstraction and analysis have to be held together: "Synthesis and analysis require each other" (26). Whitehead's particular ontology solves the problem of trying to synthesize various, unrelated substances. Because the fundamental level of reality is process or activity, an occasion's nature "consists in its relevance to other things, and its individuality consists in its synthesis of other things so far as they are relevant to it" (26).
The other mode of symbolic reference Whitehead calls "Causal Efficacy". Hume attempted to lay a groundwork for a purely empiricist notion of knowledge of sense-data. However, in his system, there is no way to account for the present being anything similar to the past. This is shown in his doctrine of causation and other places. For Hume, time is just a succession of events, apparently unrelated to one another. The question of course, is how, on an empiricist framework, the empiricist can account for the present in terms of the past. Or to put it another way, "What does the present have in common with the past?". Whitehead saw this gap in Hume's epistemology and sought his remedy through the idea of causal efficacy. Whitehead said, " . . . what is already given for experience can only be derived from that natural potentiality which shapes a particular experience . . ." If there is no connection between the past and the present, then the present is all we "have", and there is no basis for why anything remains the same, yet it always seems to. Presentational immediacy works in the realm of extension and causal efficacy works in the realm of time. The past occasions "impose" themselves upon the present: "In the mode of causal efficacy they exhibit the almost instantaneously precedent bodily organs as imposing their characters on the experience in question" (50). This is how one can be sure the present will resemble the past.
Presentational immediacy is something that happens "within" us. The abstraction involved takes place within the occasion. But causal efficacy is something that "arise[s] from without us" (58). He says, " . . . the causal efficacy from the past is at least one factor giving our presentational immediacy in the present" (58). Putting these two modes together is what Whitehead called "Symbolic Reference." He says, "The synthetic activity whereby these two modes are fused into one perception is what I have called `symbolic reference'" (18). In symbolic reference, all of the sense-data can be accounted for and put together: "By symbolic reference the various actualities disclosed respectively by the two modes are either identified, or are at least correlated together as interrelated elements in our environment" (18). In other words, symbolic reference shows us what is "there." It is by the combination of these two modes that shows one "what the actual world is for us . . ." (18).
Whether or not you agree with his epistemology (and his metaphysics for that matter - they are both closely related), you have to give Whitehead credit. This a great work in the realm of epistemology and semiotics. Though somewhat limited due to its close relation to his metaphysics, it still remains incredibly valuable.