THE NATURE OF STIMULATION 23 



cause then has itself the specific character of a condition, it is 

 itself a condition. Has it perhaps then some specific peculiarity 

 in contrast to the other conditions, which would give it a promi- 

 nent place? Experience teaches us that nothing, that is to say, 

 no state or process in the world, is dependent upon a single factor 

 alone. There are always numerous factors which bring about 

 the state or process. Would it be possible to distinguish which 

 of these particular conditions is of the greatest importance? 



First of all, it must here be taken into consideration that the 

 importance of a condition is not one which is capable of increase 

 or decrease, for the simple reason that necessity, which forms 

 an essential component of the conception of cause cannot be 

 varied. A factor cannot be more than necessary for the exist- 

 ence of a state or the taking place of a process. If, however, 

 it is less than necessary, then it is not necessary at all, and 

 the state or process exists also without it, that is to say, the 

 factor is not a condition. In other words: all conditions for a 

 state or process are of equal value for its existence, as they are 

 all necessary. 



If one attempts to prove by means of concrete examples this 

 statement obtained by purely logical deduction — a control which, 

 considering the experimental nature of modern thought, never 

 should be neglected even in the simplest of reasoning — it might 

 appear that an objection could still be made against its general 

 validity. From various instances it might be concluded that 

 there are conditions, which as such are not absolutely necessary 

 for a state or process, but can be replaced by other factors. An 

 example may serve to make this clear. I »pour diluted hydro- 

 chloric acid on powdered carbonate of sodium, and carbon dioxide 

 is set free. The addition of hydrochloric acid is here a condition 

 for the liberation of the carbon dioxide. Without the presence of 

 the hydrochloric acid the process does not occur. Nevertheless 

 I can substitute diluted sulphuric acid for the hydrochloric acid. 

 Here it would appear that one condition can be replaced by 

 another. But one must not be deceived. A closer observation 

 soon shows that the process has not been sufficiently analyzed 

 if we look upon the addition of hydrochloric acid as a condition 



