September 9, 1915] 



NATURE 



n 



the two quite distinct conceptions involved in its sub- 

 divisions into potential and kinetic energy. 



Enough has been said to show that the peculiar 

 powers necessary for the study of one of the most 

 abstruse branches of knowledge may be expressed in 

 terms which bring them down to the level at which 

 comparison with other subjects is possible. Applying 

 the same reasoning to other occupations, the same 

 conclusion is inevitable. The commercial man, the 

 politician, and the artist must all possess the type of 

 memory best suited to concentrate in the field of 

 mental vision their own experiences as well as what 

 they have learned from the experience of others; and, 

 ^further, they must have the power of selecting out of 

 multitude of possible lines of action the one that 

 ids to success ; it is this power which Poincar^ 



ills the inventive faculty. 



The argument must not be pushed too far, as it 

 > would be absurd to affirm that all differences in the 



ipability of dealing successfully with the peculiar 

 problems that occur in the various professions may 

 reduced to peculiarities of memory. I do not even 

 wish to assert that Poincar6's conclusions should be 

 accepted without qualification in the special case dis- 

 cussed by him. What is essential, to my mind, is to 

 treat the question seriously, and to dismiss the vague 

 generalities which, by drawing an artificial barrier 

 between different groups of professions, try to cure 

 real or imaginary defects through plausible though 

 quite illusory remedies. All these recommendations 

 are based on the fallacy that special gifts are asso- 

 ciated with different occupations. Sometimes we are 

 recommended to hand over the affairs of the nation 

 to men of business ; sometimes we are told that salva- 

 tion can only be found in scientific methods — what is 

 a man of business, and what is a scientific method? 

 If you define a man of business to be one capable of 

 managing large and complicated transactions, the in- 

 ference becomes self-evident ; but if it be asserted that 

 only the specialised training in commercial transactions 

 can develop the requisite faculties, the only proof of 

 the claim that could be valid would be the one that 

 would show that the great majority of successful 

 statesmen, or political leaders, owed their success to 

 their commercial experience. On the other hand, 

 every method that leads to a correct result must be 

 called a scientific method, and what requires sub- 

 stantiating is that scientific training is better than 

 other training for discovering the correct method. 

 This proof, as well as the other, has not been, and, 

 1 think, cannot be, given. When, therefore, one man 

 calls for the conduct of affairs "on business lines" 

 and the other clamours for scientific methods, they 

 either want the same thing or they talk nonsense. 

 The weak point of these assertions contrasting dif- 

 ferent classes of human efforts is that each class 

 ^r-lects its own strongest men for comparison with 



he weakest on the other side. Where technical know- 

 ledge is required, the specialist should be consulted, 

 but in questions of general policy he is seldom the best 

 judge. 



The most fatal distinction that can be made is the 

 one which brings men of theory into opposition to 

 men of practice, without regard to the obvious truth 

 that nothing of value is ever done which does not 

 involve both theory and practice ; while theory is 

 sometimes overbearing and irritating, there are among 

 those who jeer at it some to whom Disraeli's definition 

 applies : the practical man is the man who practises 

 the errors of his forefathers. With refined cruelty 

 Nemesis infects us with the disease most nearly akin 

 to that which it pleases us to detect in others. It is 

 the most dogmatic of dogmatics who tirades against 

 dogma, and only the most hopeless of theorists can 



NO. 2393, VOL. 96] 



declare that a thing may be right in theory and wrong 

 in practice. 



Why does a theory ever fail, though it may be sound 

 in reasoning? It can only do so because every 

 problem involves a much larger number of conditions 

 than those which the investigator can take into 

 account. He therefore rejects those which he believes 

 to be unessential, and if his judgment is at fault he 

 goes wrong. But the practical man will often fail for 

 the same reason. When not supported by theoretical 

 knowledge he generalises the result of an observation 

 or experiment, applying it to cases where the result 

 is determined by an altogether different set . of con- 

 ditions. To be infallible the theorist would have to 

 take account of an infinite number of circumstances, 

 and his calculations would become unmanageable, 

 while the experimenter would have to perform an 

 infinite number of experiments, and both would only 

 be able to draw correct conclusions after an infinite 

 lapse of time. They have to trust their intuition in 

 selecting what can be omitted with impunity, and, 

 if they fail, it is mainly due to the same defect of 

 judgment. And so it is in all professions : failure 

 results from the omission of essential considerations 

 which change the venue of the problem. 



Though theory and practice can only come into 

 opposition when one of them is at fault, there is 

 undoubtedly a contrast in character and temperament 

 between those wholncline more towards the one and 

 those who prefer the other aspect; some like a 

 solitary life at the desk, while others enjoy being 

 brought into contact with their fellows. There have at all 

 times been men predestined by nature to be leaders, and 

 leadership is required in all branches of knowledge — 

 the theoretical as well as the more active pursuits ; but 

 we must guard against accepting a man's estimate 

 of his own power to convert his thoughts into acts. 

 In the ordinary affairs of life a man who calls himself 

 a man of action is frequently only one who cannot 

 give any reasons for his actions. To claim that title 

 justly a man must act deliberately, have confidence 

 in his own judgment, sufficient tenacity of purpose to 

 carry it through, and sufficient courage to run the 

 unavoidable risks of possible failure. These risks may 

 be trivial or they may be all-important. They may 

 affect the reputation of one unit of creation or involve 

 the whole life of a nation, and according to the great- 

 ness of the issue we shall honour the man who, having 

 taken the risk, succeeds. But whether the scale be 

 microscopic or interstellar, the essence of the faculty 

 of blending theory and practice is the same, and both 

 men of books and men of action are to be found in 

 the philosopher's study and the laboratory, as well as 

 in the workshop or on the battlefield. Modern science 

 began, not at the date of this or that discovery, but 

 on the day that Galileo decided to publish his Dialogues 

 in the language of his nation. This was a deliberate 

 act destined to change the whole aspect of science 

 which, ceasing to be the occupation of a privileged 

 class, became the property of the community. Can 

 you, therefore, deny the claim of being a man of 

 action to Galileo, can you deny it to Pasteur, Kelvin, 

 Lister, and a host of others? There are, no doubt, 

 philosophers who cannot manage even their own 

 affairs, and whom it would be correct to call pure 

 theorists, but that proves nothing, because their defect 

 makes them worse philosophers as well as worse 

 citizens. 



In his presidential address, delivered to this 

 Association in 189^, Sir Michael Foster summarised 

 the essential features of the scientific mind. Above 

 all other things he considered that its nature should 

 be such as to vibrate in unison with what it is in 

 search of; further, it must possess alertness, and 



