Enlightenment began with an unparalleled confidence in human reason. The newscience’s success in making clear the natural world through Locke, Berkeley, andHume affected the efforts of philosophy in two ways.
The first is by locatingthe basis of human knowledge in the human mind and its encounter with thephysical world. Second is by directing philosophy’s attention to an analysis ofthe mind that was capable of such cognitive success. John Locke set the tone forenlightenment by affirming the foundational principle of empiricism: There isnothing in the intellect that was not previously in the senses. Locke could notaccept the Cartesian rationalist belief in innate ideas.
According to Locke, allknowledge of the world must ultimately rest on man’s sensory experience. Themind arrives at sound conclusions through reflection after sensation. In otherwords the mind combines and compounds sensory impressions or “ideas”into more complex concepts building it’s conceptual understanding. There wasskepticism in the empiricist position mainly from the rationalist orientation.Locke recognized there was no guarantee that all human ideas of things genuinelyresembled the external objects they were suppose to represent.
He also realizedhe could not reduce all complex ideas, such as substance, to sensations. He didknow there were three factors in the process of human knowledge: the mind, thephysical object, and the perception or idea in the mind that represents thatobject. Locke, however, attempted a partial solution to such problems. He didthis by making the distinction between primary and secondary qualities. Primaryqualities produce ideas that are simply consequences of the subject’s perceptualapparatus. With focusing on the Primary qualities it is thought that science cangain reliable knowledge of the material world. Locke fought off skepticism withthe argument that in the end both types of qualities must be regarded asexperiences of the mind.
Lockes Doctrine of Representation was thereforeundefendable. According to Berkley’s analysis all human experience isphenomenal, limited to appearances in the mind. One’s perception of nature isone’s mental experience of nature, making all sense data “objects for themind” and not representations of material substances. In effect while Lockehad reduced all mental contents to an ultimate basis in sensation, Berkeley nowfurther reduced all sense data to mental contents. The distinction, by Locke,between qualities that belong to the mind and qualities that belong to mattercould not be sustained. Berkeley sought to overcome the contemporary tendencytoward “atheistic Materialism” which he felt arose without just causewith modern science. The empiricist correctly aims that all knowledge rests onexperience. In the end, however, Berkeley pointed out that experience is nothingmore than experience.
All representations, mentally, of supposed substances,materially, are as a final result ideas in the mind presuming that the existenceof a material world external to the mind as an unwarranted assumption. The ideais that “to be” does not mean “to be a material substance;”rather “to be” means “to be perceived by a mind.” Throughthis Berkeley held that the individual mind does not subjectively determine itsexperience of the world. The reason that different individuals continuallypercieve a similar world and that a reliable order inheres in that world is thatthe world and its order depend on a mind that transcends individual minds and isuniversal (God’s mind). The universal mind produces sensory ideas in individualminds according to certain regularities such as the “laws of nature.”Berkeley strived to preserve the empiricist orientation and solve Lockesrepresentation problems, while also preserving a spiritual foundation for humanexperience. Just as Berkeley followed Locke, so did David Hume of Berkeley. Humedrove the empiricist epistemological critique to its final extreme by usingBerkeley’s insight only turning it in a direction more characteristic of themodern mind.
Being an empiricist who grounded all human knowledge in senseexperience, Hume agreed with Lockes general idea, and too with Berkeley’scriticism of Lockes theory of representation, but disagreed with Berkeley’sidealist solution. Behind Hume’s analysis is this thought: Human experience wasindeed of the phenomenal only, of sense impressions, but there was no way toascertain what was beyond the sense impressions, spiritual or otherwise. Tostart his analysis, Hume distinguished between sensory impressions and ideas.Sensory impressions being the basis of any knowledge coming with a force ofliveliness and ideas being faint copies of those impressions.
The question isthen asked, What causes the sensory impression? Hume answered None. If the mindanalyzes it’s experience without preconception, it must recognize that in factall its supposed knowledge is based on a continuous chaotic volley of discretesensations, and that on these sensations the mind imposes an order of its own.The mind can’t really know what causes the sensations because it neverexperiences “cause” as a sensation. What the mind does experience issimple impressions, through an association of ideas the mind assumes a causalrelation that really has no basis in a sensory impression. Man can not assume toknow what exists beyond the impressions in his mind that his knowledge is basedon. Part of Hume’s intention was to disprove the metaphysical claims ofphilosophical rationalism and its deductive logic. According to Hume, two kindsof propositions are possible. One view is based purely on sensation while theother purely on intellect.
Propositions based on sensation are always withmatters of concrete fact that can also be contingent. “It is rainingoutside” is a proposition based on sensation because it is concrete in thatit is in fact raining out and contingent in the fact that it could be differentoutside like sunny, but it is not. In contrast to that a proposition based onintellect concerns relations between concepts that are always necessary like”all squares have four equal sides.” But the truths of pure reason arenecessary only because they exist in a self contained system with no mandatoryreference to the external world.
Only logical definition makes them true bymaking explicit what is implicit in their own terms, and these can claim nonecessary relation to the nature of things. So, the only truths of which purereason is capable are redundant. Truth cannot be asserted by reason alone forthe ultimate nature of things. For Hume, metaphysics was just an exalted form ofmythology, of no relevance to the real world. A more disturbing consequence ofHume’s analysis was its undermining of empirical science itself.
The mind’slogical progress from many particulars to a universal certainty could never beabsolutely legitimated. Just because event B has always been seen to followevent A in the past, that does not mean it will always do so in the future. Anyacceptance of that “law” is only an ingrained psychologicalpersuasion, not a logical certainty. The causal necessity that is apparent inphenomena is the necessity only of conviction subjectively, of human imaginationcontrolled by its regular association of ideas. It has no objective basis. Theregularity of events can be perceived, however, there necessity can not. Theresult is nothing more than a subjective feeling brought on by the experience ofapparent regularity. Science is possible, but of the phenomenal only, determinedby human psychology.
With Hume, the festering empiricist stress on senseperception was brought to its ultimate extreme, in which only the volley andchaos of those perceptions exist, and any order imposed on those perceptions wasarbitrary, human, and without objective foundation. For Hume all human knowledgehad to be regarded as opinion and he held that ideas were faint copies ofsensory impressions instead of vice – versa. Not only was the human mind lessthan perfect, it could never claim access to the world’s order, which could notbe said to exist apart from the mind. Locke had retained a certain faith in thecapacity of the human mind to grasp, however imperfectly, the general outlinesof an external world by means of combining operations. With Berkeley, there hadbeen no necessary material basis for experience, though the mind had retained acertain independent spiritual power derived from God’s mind, and the worldexperienced by the mind derived its order from the same source.