336 METHODOLOGY OF SCIENCE 



vations were, the more distant the future for which he can predict. 

 All such scientific predictions are limited, therefore, with reference to 

 their number and their accuracy. If the skull shown to the zoologist 

 is that of a chicken, then he will probably be able to indicate the 

 general characteristics of chickens, and also perhaps whether the 

 chicken had a top-knot or not; but not its color, and only uncertainly 

 its age and its size. Both facts, the possibility of prediction and its 

 limitation in content and amount, are an expression for the two 

 fundamental facts, that among our experiences there is similarity, 

 but not complete agreement. 



The foregoing considerations deserve to be discussed and extended 

 in several directions. First, the objection will be made that a chicken 

 or a planet is not an experience; we call them rather by the most 

 general name of thing. But our knowledge of the chicken begins 

 with the experiencing of certain visual impressions, to which are 

 added, perhaps, certain impressions of hearing and touch. The 

 sight impressions (to discuss these first) by no means completely 

 agree. We see the chicken large or small, according to the distance; 

 and according to its position and movement its outline is very differ- 

 ent. As we have seen, however, these differences are continually 

 grading into one other and do not reach beyond certain limits; we 

 neglect to observe them and rest contented with the fact that certain 

 other peculiarities (legs, wings, eyes, bill, comb, etc.) remain and do 

 not change. The constant properties we group together as a thing, 

 and the changing ones we call the states of this thing. Among the 

 changing properties, we distinguish further those which depend 

 upon us (for example, the distance) and those upon which we have 

 no immediate influence (for instance, the position or motion): the 

 first is called the subjective changeable part of our experience, while 

 the second is called the objective mutability of the thing. 



This omission of both the subjectively and objectively changeable 

 portion of the experience in connection with the retention of the 

 constant portion and the gathering together of the latter into a 

 unity is one of the most important operations which we perform 

 with our experiences. We call it the process of abstraction, and its 

 product, the permanent unity, we call a concept. Plainly this pro- 

 cedure contains arbitrary as well as necessary factors. Arbitrary or 

 accidental is the circumstance that quite different phases of a given 

 experience come to consciousness according to our attention, the 

 amount of practice we have had, indeed according to our whole 

 intellectual nature. We may overlook constant factors and attend 

 to changeable ones. The objective factors, however, become neces- 

 sary as soon as we have noticed them; after we have seen that the 

 chicken is black, it is not in our power to see it red. Accordingly, in 

 general, our knowledge of that which agrees must be less than it 



