Sigmund Freud and B.F. Skinner are two of the most important theorists within the history of psychology and psychological development as a theory, but perhaps no two thinkers have developed psychological systems of analysis that could possibly clash with one another more vehemently. Indeed, both men would have profoundly disagreed on the most basic levels of even considering what psychology's basic function is. Sigmund Freud focused on a conception of psychology, known as psychoanalysis, in which he claimed that an observer could learn about elements of someone's mental state by speaking with them and making inferences from their observations. Freud created a concept of the unconscious and claimed that these unconscious structures were exceptionally important in defining our individual action. B.F. Skinner on the other hand, argued that the mind was not at all the proper focus of study for psychology. Rather, Skinner argued that psychology should focus only on the observable behavior of organisms in ways that were quantifiable and observable. Skinner's goal was to discover the basic ways that human behavior could be controlled and to use that capability for control to make human civilization run better and more efficiently. Sigmund Freud's new approach to psychology, known traditionally as psychoanalysis, was a radically new way of viewing the way that human beings are constructed from a mental perspective. Perhaps the most important focus and contribution that Freud added to the field of psychological inquiry was the notion of what he called the unconscious. The unconscious is that part of the mind that remains unknown and unknowable to the conscious mind in its construction of the world. He accounts for this development in his work, arguing that society required the repression of our most basic impulses and it is these repressed impulses that form the basis of our unconscious:

What happens instead, as he goes on to explain, is that those "primitive impulses," of which the sexual impulse is the strongest, are sublimated or "diverted" towards other goals that are "socially higher and no longer sexual." Our instincts and primitive impulses are thus repressed; however, Freud believed that the sexual impulse was so powerful that it continually threatened to "return" and thus disrupt our conscious functioning (hence the now-famous term, "the return of the repressed").

(Felluga)

So Freud noted not only that we are motivated and moved by forces that exist outside of our conscious cogitation and understanding, but also developed a theoretical explanation for how and why these unconscious elements existed. Freud argued that the primary drive for human interaction was, at its base, sexual, and that the majority of repressed and unconscious motivations were different sublimations of a primal sexual impulse that society had necessarily and understandably required to be repressed.

In further developing his systems of the unconscious, Freud named the primary mechanisms that shape and effect the development and interaction of the unconscious. The most important of these two forces are known by the names of the "ego" and the "id." The id can be defined as the place in which are old impulses are stored:

The id is the great reservoir of the libido, from which the ego seeks to distinguish itself through various mechanisms of repression. Because of that repression, the id seeks alternative expression for those impulses that we consider evil or excessively sexual, impulses that we often felt as perfectly natural at an earlier or archaic stage and have since repressed. The id is governed by the pleasure-principle and is oriented towards one's internal instincts and passions. Freud also argues on occasion that the id represents the inheritance of the species, which is passed on to us at birth; and yet for Freud the id is, at the same time, "the dark, inaccessible part of our personality."

(Felluga)

So the central conflict occurred in Freud's notion of the consciousness between the Id, which was the store of these most basic primal desires, and the ego, which, reinforced by society, seeks to separate itself from the most base notions and in someway overcome or at least sublimate them in some fashion. Freud developed several other theories in accordance with these ideas, perhaps the most famous of which is the Oedipal Complex, in which Freud argued that young males feel a basic primal sexual competition with their fathers for possession of their mother, but that they repress this feeling because of societal constraints. Freud claimed that mechanisms such as these were formative and deeply affected and individual not only throughout their development, but also in their adulthood as well.

While Freud's contributions to theoretical understandings of psychology, particularly in his understanding and development of the concept of the unconscious,...

Freud, according to many, often tended to develop his ideas about the structures underlying human psychology without any real scientific basis, and form there he often then used these already assumed psychological functions to make other insights, suggesting that much of his work was based on a shaky structure of assumption rather than observation and induction. He has come under considerable criticism from feminist critics in particular that argue very reasonably that his interpretations of women and "hysteria" were extremely problematic and very likely had much more to do with the cross-section of the public that he had access to rather than any essential feature of female psychology. Essentially, while Freud made some very important contributions, he often ignored the basics of the scientific method, which deeply undermined the "scientific" basis of his claims. Indeed, later theorists would attempt to create a type of psychology that was more inherently and realistically scientific. Behaviorism is one such example, in which a group of psychologists completely disputed Freud's definition of psychology as a science of the mind, concluding instead that it was the business of psychology only to investigate observable behaviors that could then be scientifically quantified.
B.F. Skinner was another extremely important psychological theorist of the twentieth century whose ideas were exceptionally influential for a period of time, although most of his larger conclusions and the greater theoretical framework surrounding most of his discoveries have since been discredited as either problematic, incorrect, or not backed by proper scientific evidence. Nonetheless, Skinner remains an important and imposing figure within the history of psychology. Skinner was and is typically associated with the psychological school that is known as behaviorism. Behaviorism was a science that was radically different than the psychoanalysis that had gone before it. Instead of envisioning and analyzing the complex psychological mechanisms that Freud had envisioned, Behaviorists believed that psychology should be purely scientific and study only those phenomena that were absolutely observable and quantifiable in an organism -- behavior. Basically, Behaviorism held to three central tenets:

(1) Psychology is the science of behavior. Psychology is not the science of mind.

(2) Behavior can be described and explained without making reference to mental events or to internal psychological processes. The sources of behavior are external (in the environment), not internal (in the mind).

(3) In the course of theory development in psychology, if, somehow, mental terms or concepts are deployed in describing or explaining behavior, then either (a) these terms or concepts should be eliminated and replaced by behavioral terms or (b) they can and should be translated or paraphrased into behavioral concepts

(Graham)

So behaviorism was, in fact an attempt to make psychology into a field that was subject to the same sort of rigor and the same sort of induction that traditional "hard" sciences such as physics are. The prime differentiation between behaviorism and psychoanalysis is that behaviorism argues that psychology is primarily not a science of the mind, but one that observes quantifiable actions by organisms -- behavior. It was also a radically reductionist methodology, because all of the psychological terms that assumed a motivation from consciousness or inner thinking, were redefined in behavioral terms.

Part of the problem with Skinner's work in behavioral fields is that, in keeping with the above theory, he refused to consider internal differences in reasoning capability between animals. As a result, he tended to equate the behavior of rats with that of humans and assume that parallels could be successfully drawn between the two. Of course, since the physiological differences between the two are enormous, this proved extremely problematic for behaviorism's coherence as a theory. Furthermore, Skinner, in refusing to consider mental elements, did not think about the issue that "interpretation" of behavioral data was not scientific necessarily, but could be very much affected by the assumptions and predilections of the observer.

Skinner and the other Behaviorists essential held the theory that humans, like all other animals, were completely ruled by the interaction of stimulus and response, which was the very hallmark of what is considered to be life. Skinner, however, extended this idea to its furthest conclusion, arguing that humans were essentially no more than a series of responses to stimuli and therefore they had no mind, no real inner mental…