140 INTRODUCTION TO PHILOSOPHY OF SCIENCE 



the sub- and super-ordination of classes have not been 

 established, and special laws have not been shown to be 

 cases of more highly abstract laws. Any element of the 

 scheme might be modified or taken from it without seriously 

 influencing the remaining elements; a novel feature might be 

 added without necessitating any changes within the body of 

 symbols. 



The best way to describe this feature is to suggest that 

 the order of elements in an empirical science is that of 

 acquisition rather than of demonstration. The propositions 

 take on the order in which they have been discovered, 

 rather than the order in which they could be deduced. 

 The order of discovery, however, is more or less accidental, 

 and might have been otherwise; but the order of logical 

 deducibility is a fixed one: premise is always more basic 

 than conclusion. Descriptive science is quite without deduc- 

 tive organization; the distinction between derived and un- 

 derived propositions has not yet arisen. All propositions 

 are on the same level logically; no proposition is the ground 

 of another. Propositions in descriptive science merely follow 

 one another; they do not follow from one another. No 

 element of the totality, therefore, determines any other 

 element; the elements are independent of one another, and 

 the complex is an aggregate rather than a system. 



An illustration of the difference between the order of the 

 acquisition of propositions, which is descriptive of the struc- 

 ture of empirical science, and the order of the deduction of 

 propositions, which is descriptive of the structure of rational 

 science, is to be found in the distinction between a scientific 

 biography and a scientific textbook. If a scientist were to 

 write his autobiography he would describe his discoveries 

 in the order in which they occurred to him. Chapter I 

 would disclose the conclusions of his early period; Chapter II 

 would indicate how his reflections were turned in a certain 

 direction by these results, and how he was led to perform 

 experiments of a certain kind; Chapter III might show 

 how these conclusions led him to modify the formulations 



