1750 - Hume - the caged mind.

David Hume (1711-1776) synthesised the ideas of Locke and Berkeley. He formulated the most forthright version of empiricism. Hume stated that all contents of mind are solely built from sense experiences. Like Locke, he distinguished between impressions and ideas. Hume held that the mind associates ideas with one another on account of three qualities: resemblance, contiguity, and causation. His position was that reason and rational judgments are merely habitual associations of distinct sensations or experiences. Although he considered the notion of cause and effect as the basis of knowledge, he held that causality is merely inferred by the mind: "Reason can never show us the connexion of one object with another, tho’ aided by experience, and the observation of their conjunction in all past instances." This extreme empiricism led Hume to argue that we cannot achieve certainty about external reality, but only about the inner world of our perceptions and thoughts. Hence, there can neither be certitude about the existence of the self, the physical world, or even God.

1750 - Kant - the Copernican revolution in epistemology.

The time was ripe for Immanuel Kant's (1724-1804) famous writing, Critique of Pure Reason, in which he investigated and criticised the epistemological propositions of Hume and his predecessors. Kant rejected Hume's extreme empiricism and proposed that there is more to knowledge than bare sense experience. He distinguished between "a posteriori" and "a priori" knowledge, the former being derived from perception, hence, occurring after (post) perception, and the latter being a property of thought, independent of experience and existing before (prior to) experience. Knowledge is expressed in judgments, which -according to Kant- are operations of thought that connect a subject with a predicate. The predicate qualifies the subject in some way. There are many examples for a posteriori judgments, such as "the apple is red" or "the music is loud." Since a posteriori judgments are solely based on data supplied by the senses, they can be denied without contradiction. In contrast, a priori judgments cannot be denied without contradiction, because they are based on logic rather than perception.

While all a posteriori (empirical) judgments are automatically synthetic, Kant discerned two types of a priori judgments, analytic and synthetic judgments. He said, "necessity and strict universality are sure marks of a priori knowledge." In an analytic a priori statement, the predicate is already contained in the subject, such as in: "all triangles have three angles," or, "all bodies are extended." In contrast, synthetic a priori judgments are compound and are often found in mathematics and science, as for example: "a straight line is the shortest connection between two points," and, "for every action there is an equal an opposite reaction." The latter statement -the third law of Newtonian mechanics- may at first be mistaken for an a posteriori statement, but it isn't, because we haven't yet experienced every mechanical action.

Kant furthermore distinguished between concepts, which are derived from thought, and particulars which are derived from sense experience. The idea of a winged horse is an example of a synthetic concept derived from the particulars of wings and horses. Particulars are always a posteriori (empirical), with the exception of two, namely space and time, which are a priori and thus, provide the basis for other (synthetic) a priori propositions. There are also a priori concepts, which Kant calls categories, of which there are twelve, namely unity, plurality, totality, reality, negation, limitation, substance, causality, interaction, possibility, existence, and necessity. Kant maintained that these concepts are not derived empirically, but that the mind applies them to all perception and that they are therefore a priori. In this way, the a priori particulars and concepts form the basis of knowledge. What exists apart from them, Kant calls the "things in themselves", the noumenal reality, which is purely intelligible and non-sensual, as opposed to the phenomenal reality, which is perceivable. Since the things in themselves cannot be known directly, according to Kant, human knowledge must forever remain limited.

1800 - Gall - the charted brain.

Franz Gall (1758-1828) began the localisation of functions in the brain. He distinguished areas that he thought were responsible for speech, hearing, motor control, and so forth. Gall maintained, "that the brain was composed of as many organs as the individual had faculties, tendencies and feelings." [Ackerknecht, 1958, p150]. It was this approach from which sprang the now discredited practice of phrenology. Nevertheless, Gall discovered a great deal about the anatomy of the brain. He placed the main faculties in the cortex and established the concept of nerve pathways. Gall described the clefts between the grey matter as nerve matrices and the white matter as having a conductor function.

During the 19th century evidence accumulated to show that the brain could continue to operate, despite the loss of various parts of its substance. This was verified by the study of the consequences of cutting differentiable parts of the brain in animals and through the investigation of brain injuries and brain diseases in humans. The new evidence slowly led to the view that the mind dwelt in the whole of the brain, as opposed to particular anatomical locations, and thus, consciousness was understood as a function of the entirety of the human brain.

1800 - Hegel - the evolving world mind.

Georg Wilhelm Friedrich Hegel (1770-1831) accomplished what Kant had declared impossible. According to Hegel, mind is capable of arriving at full knowledge about things in themselves. He formulated a dialectical method, according to which knowledge pushes forwards to greater certainty, and ultimately towards knowledge of the noumenal world. He said that ultimate reality is absolute mind, reason, or spirit, which manifests itself in history and in the universe. Hegel set forth the proposition, "what is real is rational and what is rational is real," and from this he concluded that everything that is, is knowable. The world mind (Weltgeist) is universal; the rational activities of individuals are therefore instances of the Absolute. The self-development of mind is the result of evolving idea systems, a process that he called the dialectical processes of thesis and antithesis. According to Hegel, an idea, a thesis, always contains incompleteness, and thus, yields a conflicting idea, an antithesis. In a higher-level theory, a third point of view, the synthesis, arises that provides the solution. The synthesis overcomes the conflict between thesis and antithesis by reconciling the truth contained in both at a higher level of insight. The synthesis then becomes a new thesis that is subsequently confronted by another antithesis, and so forth. By this dialectical method, the collective mind, namely that of a group, society, nation and ultimately the world, advances towards the perfection of its knowledge.

1800 - Mill - psychology takes shape.

James Mill (1773-1836), father of John Stuart Mill, investigated in his book Analysis of the Phenomena of Mind topics such as feeling, sensation, consciousness, associations, and thus became a precursor of modern psychological studies.

1850 - Darwin - the evolution of our species.

Charles Robert Darwin (1809-1882) formulated the modern theory of the evolution of species. The discoveries he made while aboard the HMS Beagle on an expedition around the world, impelled him to write his famous book, On the Origin of Species. In this writing Darwin developed the concepts of hereditary variation, speciation, and natural selection. Although Darwin did not touch upon psychology or epistemology, his influence was so fundamental that it affected almost any branch of science; consequently, it also affected the contemporary understanding of mind. Since the brain is the organ of mind, it follows that the forming of mind must have gone hand in hand with the evolution of the human brain. Mind is therefore a product of evolution, just as man is.

1850 - Galton - the wellborn mind.

The British inventor Francis Galton (1822-1911) advocated the idea that human traits, or properties of human mind in general, are inherited and can therefore be altered and improved by selective breeding. He held that mental qualities, such as intelligence, memory capability, etc., can be measured objectively, but failed in his efforts to provide methods for quantitative measurement. Galton also coined the term "nature and nurture", which is still heatedly debated today. Laying the foundations for eugenics, he explained: "I have no patience with the hypothesis occasionally expressed, and often implied, especially in tales written to teach children to be good, that babies are born pretty much alike, and that the sole agencies in creating differences between boy and boy, and man and man, are steady application and moral effort. It is in the most unqualified manner that I object to pretensions of natural equality."

1850 - Huxeley - mind caused, but not causing.

Thomas Henry Huxeley (1825-1895) was a zoologist advocating Darwinism. He regards consciousness as a collateral effect of certain physical causes, and only an effect, but never a cause.

1850 - Wundt - the father of psychology.

Wilhelm Max Wundt (1832-1920) is often credited with establishing psychology as a field of scientific studies independent from philosophy. He carried out extensive experimental research on stimuli, perception, and feeling. Wundt's structural psychology stresses observation of the modes of conscious mind, rather than making philosophical inferences about the nature of mind and, hence, takes a wholly scientific approach.

1900 - James - mind as a stream of consciousness.

William James (1842-1910) established the American philosophical school of pragmatism. He was a philosopher as much as a psychologist. In his pragmatic philosophy, he emphasised the applicability and practical utility of concepts and theories. James declared most metaphysical theories as meaningless, because they are neither testable, nor do they deal with existential problems. His innovative work, The Principles of Psychology, investigates the functions of the brain, consciousness, conception, memory, and association. James pointed out that we have a sense of a personal consciousness, and that it is ours, not something that we share with others. Later psychologists referred to it as the "I".

James also held that our states of consciousness are always changing. We have a sense of temporal continuity in consciousness, which leads to the conception of a stream of consciousness. The mind has a function of memory that allows us to recall experiences and ideas. Moreover, consciousness is selective of what it pays attention to. James formulated a materialistic view of mind, which -in some sense- anticipates the modern view of neuroscience and psychobiology. "Taking all such facts together, the simple and radical conception dawns upon the mind that mental action may be uniformly and absolutely a function of brain-action, varying as the latter varies, and being to the brain-action as effect to cause." [James, 1892, pp5-6]