Later German systems，had he heard of them，would have been summarily rejected by him as so much transcendental moonshine.The problem of philosophy was，he held，a very simple one，if attacked in a straightforward，scientific method.
Mill，like his Scottish rivals，applies 'Baconian'principles.The inductive method，which had already been so fruitful in the physical sciences，will be equally effective in philosophy，and ever since Locke，philosophy had meant psychology，the 'philosophy of the mind'and the philosophy of the body may be treated as co-ordinate and investigated by similar methods，in the physical sciences we come ultimately to the laws of movement of their constituent atoms.
In the moral sciences we come in the same way to the study of 'ideas，'the questions，How do ideas originate？and how are they combined so as to form the actual state of consciousness？are therefore the general problems to be solved.Hume had definitely proposed the problem.Hartley had worked out the theory of association of ideas which Hume had already compared 45to the universal principle of gravitation in the physical world；and had endeavoured to show how this might be connected with physiological principles.
Hartley's followers had been content to dwell upon the power of association.
Abraham Tucker，Priestley，Erasmus Darwin，and Belsham represented this tendency，and were the normal antagonists of Reid and Stewart.In France the 'ideologists'mainly followed Condillac，and apparently knew nothing of Hartley.Mill，as his son testifies，had been profoundly influenced by Hartley's treatise --the 'really master-production，'as he esteemed it，'in the philosophy of mind.'46Hartley's work，as the younger Mill thought，and the elder apparently agreed，was very superior to the 'merely verbal generalisation of Condillac.'James Mill，however，admired Condillac and his successors.In his article upon education，Mill traces the association theory to Hobbes，Locke，and Hume，the last of whom，he says，was succeeded by the two 'more sober-minded'philosophers，Condillac and Hartley；while he especially praises Erasmus Darwin，Helvétius，and Cabanis.Mill，therefore，may be regarded as an independent ally of the ideologists whose influence upon Brown has been already noticed.Mill had not read Brown's Lectures when he began his Analysis，and after reading them thought Brown 'but poorly read in the doctrine of association.'47He had，however，read the essay upon causation，which he rather oddly describes as 'one of the most valuable contributions to science for which we are indebted to the last generation.'48He accepted Brown's view minus the 'intuition.'
The pith of Mill's book is thus determined.His aim is to give a complete analysis of mental phenomena，and therefore to resolve those phenomena into their primitive constituent atoms.Here we have at once a tacit assumption which governs his method.
Philosophy，speaking roughly，is by some people supposed to start from truths，and thus to be in some way an evolution of logic.According to Mill it must start from facts，and therefore from something not given by logic.To state clearly，indeed，the relation between truth and fact may suggest very intricate problems.Mill，at any rate，must find a basis in fact，and for him the ultimate facts must be feelings.The reality at least of a feeling is undeniable.The Penser c'est sentir.or the doctrine that all 'ideas'are transformed sensations is his starting-point.The word 'feeling，'according to him，includes every 'phenomenon of the mind.''think，'he says elsewhere，49does not include all our experience，but 'there is nothing to which we could not extend the term "I feel."'He proceeds to infer that our experience is either a knowledge of the feelings separately，or 'a knowledge of the order in which they follow each other；and this is all.'We may add that the knowledge is the feeling，Reid，Kant，and the Germans have indeed tried to show that there are feelings not derived from the sensations，but this，as Hartley and Condillac have shown，is a mistake.This is his first principle in a nutshell，and must give a clue to the various applications.
The next step is familiar.
Hume had distinguished impressions and ideas.'Ideas'are copies of previous 'impressions.'It is for psychology to say what are the laws by which they are related to their originals.The ultimate origin cannot be explained by psychology alone.Impressions are caused by the outward world acting in some way upon the mind and the psychologist can only classify the various modes in which they present themselves.Mill therefore begins by the usual account of the five senses，through which comes all knowledge of the external world.He adds to Reid's list muscular sensations，and those derived from the internal organs，to which last Cabanis in particular had called attention.
So far he is following the steps of his predecessors.He is，he says，simply asserting an 'indisputable'fact.50We have sensations and we have ideas，which are 'copies of sensations.'We may then consider how far these facts will enable us to explain the whole series of mental phenomena.
'Ideation，'which he suggests as a new word --the process by which a continuous series of thoughts goes on in our minds --is the general phenomenon to be considered.Without，as yet，pronouncing that sensations and copies of sensations will turn out to form the whole contents of our consciousness，he tries to show for what part of those contents they will account.
Here we come to the doctrine which for him and his school gave the key to all psychological problems.