It is important at first to identify the fact that "empiricism" may refer to a method -- for example, the "empirical method" of observing child behavior, or an "empirical study of cancer in rats" -- and it also may refer to the philosophy (or the theory) that embraces empiricism. That philosophy of empiricism, by one definition, "has its roots in dualist theories of perception and communication" (Vesey, 1976). The "perception" part of the theory, Vesey explains (vii), is when a person's mind, "as well as his body, is acted on when he perceives something." That is to say, that "something" that his body is acted upon -- let's say it is a large tree swaying in the wind -- stimulates his sense organs and his nervous system; but beyond that stimulation, there is also a "sensation" or a "sense-impression" which happens when the mind is acted on, according to the theory.
'All knowledge is founded" on these "sense-impressions" which work with the "inner awareness of the operations of the mind (remembering, discerning, reasoning, etc.)," according to Vesey's book, Impressions of Empiricism.
Another author, Stephen Davies (Empiricism and History), who writes in a very straight-forward style, asserts that "Empiricism is the belief that true knowledge comes only from sensory experience" (3), and that there are "broad destructive implications" associated with this belief. That "destructive" implication, Davies explains, exists because the historic view of empiricism (presented in the sentence above) " ... means that knowledge is not the same as belief or opinion ... [and] not the same thing as certainty, no matter how passionately felt."
But beyond that, on page 4 of his Introduction, Davies asserts that empiricism "does not mean that theory or hypothesis has no place in knowledge or the discovery of knowledge." In fact, he continues, empiricism means that knowledge "derived from experience trumps hypothesis or theory."
Meanwhile, one the most respected / revered founders of empiricism, George Berkeley, explains his concept of empiricism in Principles of Human Knowledge (53-54) in lengthy narrative that requires a good deal of patience and study for the lay person to fully grasp. Beyond the obvious things ("objects of human knowledge") in the world which we as humans have the ability to see, touch, smell, Berkeley writes that there exists an ability, "perceiving," which we also possess: "This perceiving, active being is what I call mind, spirit, soul or my self." The existence of an idea, Berkeley explains, "consists in being perceived."
Berkeley goes on in almost impossible-to-understand narrative, but the essence of his philosophy and theory is that "houses, mountains, rivers ... " all have "an existence natural or real, distinct from their being perceived by the understanding." And yet, he asks, do those objects he mentioned -- which are "the things we perceive by sense" -- exist if they are "unperceived"?
Later in his "Part 1" (65), Berkeley assures the reader that he is not arguing "against the existence of any one thing that we can apprehend, either by sense or reflection." The things he sees "with my eyes" and touches "with my hands" do very much exist, "really exist," he explains. But the things "whose existence we deny, is that which philosophers call matter or corporeal substance." He says in the next paragraph that readers should not take from his explanation that certain "things" do not exist; rather, and he insists he has presented this material "in the plainest terms I could think of," some things are more real that others.
The "spiritual substances, minds, or human souls," which can "excite ideas in themselves at pleasure," are what Berkeley considers "faint, weak, and unsteady in respect of others ... perceived by sense." But things perceived by the senses, and not the mind and spirit, have "more reality" to them because "according to certain rules of laws of nature," those things perceived by sight, touch, etc., are more "orderly, and distinct, and ... are not fictions of the mind."
The sun that Berkeley sees "is the real sun," but that which he imagines by night "is the idea of the former." If there are those who don't accept his view, he says they should "look into their own thoughts and see."
And the above paragraphs describe -- in fairly plain though sometimes esoteric language -- the prevailing definition of empiricism, which is, according to Davies (1), that "true knowledge of the world comes ultimately from sense impressions." Davies writes that empiricism evolves from epistemology, which an answer to the question, "What do we know (or can we know) and how do we know it?"
Thesis -- Empiricism May Well Evolve into Subjective Idealism
As to the question -- "Can empiricism, if followed consistently, collapse into idealism?" -- a careful reading of both empiricism and idealism may lead a writer to say "yes," but with certain reservations. Is the question related to "idealism" it its pure form? Or is the question directly connected to "subjective idealism"?
Certainly, on the surface it would appear confusing that in his Treatise Concerning the Principles of Human Knowledge, Berkeley wrote that things perceived by the senses -- and not things of the mind and spirit -- have "more reality" to them; and yet, he is credited with "the advancement of what has come to be called 'subjective idealism'" (Wikipedia, 2004). The "free encyclopedia" (Wikipedia) defines "Idealism" in philosophy as "any theory positing the primacy of spirit, mind, or language over matter." Moreover, with an idealist philosophy comes the claim that "thought has some crucial role in making the world the way it is -- that thought and the world are made for one another, or that they make one another."
Davies writes (38) that like empiricism, idealism is "a theory of knowledge," and idealism "can be traced back to the ancient Greeks, particularly Plato." And, Davies continues, the underlying principle of idealism "is simple": knowledge of the world "depends not on experience, but on ideas or the structure of the mind that observes it." That would seem contrary to Berkeley's view of empiricism, which basically stated that the experience of sense, the hearing, seeing, touching, were more "real" than thinking about something or picturing something.
This difference between idealism as defined by Davies and empiricism as seen and described by Berkeley is what initially causes one to pause before saying empiricism may be linked to, or may become, idealism.
Looking at another aspect of the issue, the Encyclopedia Britannica's definition of "subjective idealism" is a philosophy " ... based on the premise that nothing exists except minds and spirits and their perceptions or ideas." Further, a person "experiences material things, but their existence is not independent of the perceiving mind; material things are thus mere perceptions," the Britannica definition concludes.
Basically, the definition of "subjective idealism" is that nature has no existence, or in specific, nature has no objective existence, beyond what the mind can perceive of it. Perhaps it is splitting hairs, and bogging down into semantics, to attempt to separate pure idealism from subjective idealism, albeit it seems worthy to clear the air as to those two theories.
But meanwhile, in the book Impressions of Empiricism, referenced earlier in the paper, Alan Hobbs (109-110) writes that "Empiricism has, in a long tradition, oscillated between the unsatisfactory alternatives of Idealism and the Causal Theory of Perception." Hobbs asserts that the "oscillation" is due to the existence of "two apparently conflicting thoughts." One is that "sensory states are independent of, and caused by, the objects about which they provide knowledge." And the second thought, which "pushes the empiricist into the arms of Idealism," is that "claims about the world can be understood and justified only in terms of remarks exclusively about our sensory states."
Conclusion: Clearly, there are differences between what we read in terms of Berkeley's view of empiricism, and other views of idealism. But in the end, the world of empiricism seems to have idealism built within it, because, as Berkeley writes in The Preface2 (117): "It is not enough, that we see and feel, that we taste and smell a thing. Its true nature, its absolute external entity, is still concealed." And, he continues, "though it be the fiction of our own brain, we have made it [the true nature] inaccessible to all our faculties." (Idealism is, this paper explained earlier, any theory putting spirit, mind, over matter. By putting the "true nature" in a place higher than commonality, he idealizes.)
Moreover, in the respected Web pages which reprint Philosophic writings from the great minds of the last five hundred years, George Berkeley's name appears under both "idealism" and "empiricism." In fact, in the Internet Encyclopedia of Philosophy, it states that Berkeley "was one of the three most famous eighteenth century British Empiricists ... " (along with John Locke and David Hume). The motto that Berkeley espoused was "esse is percpip," or, "to be is to be perceived" (Internet Encyclopedia of…