According to J.S.Mill,James Mill and Stewart represented opposite poles of philosophic thought.I shall have to consider this dictum hereafter.On the points already noticed Stewart must be regarded as an ally rather than an opponent of the Locke and Hume tradition.Like them he appeals unhesitatingly to experience,and cannot find words strong enough to express his contempt for 'ontological'and scholastic methods.His 'intuitions'are so far very harmless things,which fall in with common sense,and enable him to hold without further trouble the beliefs which,as a matter of fact,are held by everybody.They are an excuse for not seeking any ultimate explanation in reason.He is,indeed,opposed to the school which claimed to be the legitimate successor to Locke,but which evaded Hume's scepticism by diverging towards materialism.The great representative of this doctrine in England had been Hartley,and in Stewart's day Hartley's lead had been followed by Priestley,who attacked Reid from a materialist point of view,by Priestley's successor,Thomas Belsham,and by Erasmus Darwin.We find Stewart,in language which reminds us of later controversy,denouncing the 'Darwinian School'(37)for theories about instinct incompatible with the doctrine of final causes.It might appear that a philosopher who has re-established the objective existence of space in opposition to Berkeley,was in danger of that materialism which had been Berkeley's bugbear.But Stewart escapes the danger by his assertion that our knowledge of matter is 'relative'or confined to phenomena.Materialism is for him a variety of ontology,involving the assumption that we know the essence of matter.To speak with Hartley of 'vibrations,'animal spirits,and so forth,is to be led astray by a false analogy.We can discover the laws of correspondence of mind and body,but not the ultimate nature of either.(38)Thus he regards the 'physiological metaphysics of the present day'as an 'idle waste of labour and ingenuity on questions to which the human mind is altogether incompetent.'(39)The principles found by inductive observation are as independent of these speculations as Newton's theory of gravitation of an ultimate mechanical cause of gravitation.
Hartley's followers,however,could drop the 'vibration'theory;and their doctrine then became one of 'association of ideas.'To this famous theory,which became the sheet-anchor of the empirical school,Stewart is not altogether opposed.We find him speaking of 'indissoluble association'in language which reminds us of the Mills.(40)Hume had spoken of association as comparable to gravitation --the sole principle by which our 'ideas'and 'impressions'are combined into a whole;a theory,of course,corresponding to his doctrine of 'belief'as a mere custom of associating.Stewart uses the principle rather as Locke had done,as explaining fallacies due to 'casual associations.'
It supposes,as he says,the previous existence of certain principles,and cannot be an ultimate explanation.The only question can be at what point we have reached an 'original principle,'and are therefore bound to stop our analysis.(41)Over this question he glides rather too lightly,as is his custom;but from his point of view the belief,for example,in an external world,cannot be explained by association,inasmuch as it reveals itself as an ultimate datum.
In regard to the physical sciences,then,Stewart's position approximates very closely to the purely 'empirical'view.When we come to a different application of his principles,we find him taking a curiously balanced position between different schools.'Common sense'naturally wishes to adapt itself to generally accepted beliefs;and with so flexible a doctrine as that of 'intuitions'it is not difficult to discover methods of proving the ordinary dogmas.Stewart's theology is characteristic of this tendency.He describes the so-called a priori proof,as formulated by Clarke.But without denying its force,he does not like to lay stress upon it.He dreads 'ontology'too much.He therefore considers that the argument at once most satisfactory to the philosopher and most convincing to ordinary men is the argument from design.The belief in God is not 'intuitive,'but follows immediately from two first principles:the principle that whatever exists has a cause,and the principle that a 'combination of means implies a designer.'(42)The belief in a cause arises on our perception of change as our belief in the external world arises upon our sensations.The belief in design must be a 'first principle'because it includes a belief in 'necessity'which cannot arise from mere observation of 'contingent truths.'(43)Hence Stewart accepts the theory of final causes as stated by Paley.Though Paley's ethics offended him,he has nothing but praise for the work upon Natural Theology.(44)Thus,although 'common sense'does not enable us to lay down the central doctrine of theology as a primary truth,it does enable us to interpret experience in theological terms.In other words,his theology is of the purely empirical kind,which was,as we shall see,the general characteristic of the time.
In Stewart's discussion of ethical problems the same doctrine of 'final causes'assumes a special importance.Stewart,as elsewhere,tries to hold an intermediate position;to maintain the independence of morality without committing himself to the 'ontological'or purely logical view;and to show that virtue conduces to happiness without allowing that its dictates are to be deduced from its tendency to produce happiness.His doctrine is to a great extent derived from the teaching of Hutcheson and Bishop Butler.