To confute intuitionists and get rid of intuitions was one main purpose of all Mill's speculations.What,then,is an 'intuition'?To explain that fully it would be necessary to write once more that history of the philosophical movement from Descartes to Hume,which has been summarised and elucidated by so many writers that it should be as plain as the road from St.Paul's to Temple Bar.I am forced to glance at the position taken by Reid and Stewart because it has a most important bearing upon the whole Utilitarian scheme.
Reid's main service to philosophy was,in his own opinion,(18)that he refuted the 'ideal system'of Descartes and his followers.That system,he says,carried in its womb the monster,scepticism,which came to the birth in 1739,(19)the date of Hume's early Treatise.To confute Hume,therefore,which was Reid's primary object,it was necessary to go back to Descartes,and to show where he deviated from the right track.In other words,we must trace the genealogy of 'ideas.'Descartes,as Reid admitted,had rendered immense services to philosophy.He had exploded the scholastic system,which had become a mere mass of logomachies and an incubus upon scientific progress.He had again been the first to 'draw a distinct line between the material and the intellectual world';(20)and Reid apparently assumes that he had drawn it correctly.One characteristic of the Cartesian school is obvious.Descartes,a great mathematician at the period when mathematical investigations were showing their enormous power,invented a mathematical universe.Mathematics presented the true type of scientific reasoning and determined his canons of inquiry.The 'essence'of matter,he said,was space.The objective world,as we have learned to call it,is simply space solidified or incarnate geometry.
Its properties therefore could be given as a system of deductions from first principles,and it forms a coherent and self-subsistent whole.Meanwhile the essence of the soul is thought.Thought and matter are absolutely opposed.
They are contraries,having nothing in common.Reality,however,seems to belong to the world of space.The brain,too,belongs to that world,and motions in the brain must be determined as a part of the material mechanism.
In some way or other 'ideas'correspond to these motions;though to define the way tried all the ingenuity of Descartes'successors.In any case an idea is 'subjective':it is a thought,not a thing.It is a shifting,ephemeral entity not to be fixed or grasped.Yet,somehow or other,it exists,and it 'represents'realities;though the divine power has to be called in to guarantee the accuracy of the representation.The objective world,again,does not reveal itself to us as simply made up of 'primary qualities';we know of it only as somehow endowed with 'secondary'or sense-given qualities:
as visible,tangible,audible,and so forth.These qualities are plainly 'subjective';they vary from man to man,and from moment to moment:they cannot be measured or fixed;and must be regarded as a product in some inexplicable way of the action of matter upon mind;unreal or,at any rate,not independent entities.
In Locke's philosophy,the 'ideas,'legitimate or illegitimate descendants of the Cartesian theories,play a most prominent part.Locke's admirable common-sense made him the leader who embodied a growing tendency.The empirical sciences were growing;and Locke,a student of medicine,could note the fallacies which arise from neglecting observation and experiment,and attempting to penetrate to the absolute essences and entities.Newton's great success was due to neglecting impossible problems about the nature of force in itself 'action at a distance'and so forth --and attention to the sphere of visible phenomena.The excessive pretensions of the framers of metaphysical systems had led to hopeless puzzles and merely verbal solutions.Locke,therefore,insisted upon the necessity of ascertaining the necessary limits of human knowledge.All our knowledge of material facts is obviously dependent in some way upon our sensations --however Meeting or unreal they may be.Therefore,the material sciences must depend upon sense-given data or upon observation and experiment.Hume gives the ultimate purpose,already implied in Locke's essay,when he describes his first treatise (on the title page)as an 'attempt to introduce the experimental mode of reasoning into moral subjects.'Now,as Reid thinks,the effect of this was to construct our whole knowledge out of the representative ideas.The empirical factor is so emphasised that we lose all grasp of the real world.Locke,indeed,though he insists upon the derivation of our whole knowledge from 'ideas,'leaves reality to the 'primary qualities'without clearly expounding their relation to the secondary.But Berkeley,alarmed by the tendency of the Cartesian doctrines to materialism and mechanical necessity,reduces the 'primary'to the level of the 'secondary,'and proceeds to abolish the whole world of matter.We are thus left with nothing but 'ideas,'and the ideas are naturally 'subjective'and therefore in some sense unreal.Finally Hume gets rid of the soul as well as the outside world;and then,by his theory of 'causation,'shows that the ideas themselves are independent atoms,cohering but not rationally connected,and capable of being arbitrarily joined or separated in any way whatever.Thus the ideas have ousted the facts.We cannot get beyond ideas,and yet ideas are still purely subjective.The 'real'is separated from the phenomenal,and truth divorced from fact.The sense-given world is the whole world,and yet is a world of mere accidental conjunctions and separation.That is Hume's scepticism,and yet according to Reid is the legitimate development of Descartes''ideal system.'Reid,I take it,was right in seeing that there was a great dilemma.