MICHIGAN ACADEMY OF SCIENCE. 
14 <) 
such tremendous consequence in physiology as exists between Culex, Ano- 
pheles and Stegomyia. The common mosquito which is only a nuisance, 
the other the bearer of malaria, and the third the devastating disseminator 
of yellow fever. I have known a professor of biology in a great university, 
to teach his classes to call Pectinatella an alga. It is unsafe to generalize 
without definite knowledge, and ludicrous errors multiply when scientific 
methods are abandoned for prospects believed to be more alluring. 
My third proposition is that the study of types is necessary for the purpose 
of economizing effort. This is merely a corollary to our discussion of classi- 
fication. I doubt if there is a more important principle in education than 
the one indicated by the phrase economy of effort. I believe it can be shown 
that the essential difference between the great intellect and the common 
one is embodied in the phrase economy of effort, and that the most impor- 
tant mental processes are those that most efficiently conserve mental work. 
A type from its very nature stands for a class. Everything that we may 
predicate of the type as distinguished from the individual, we may predicate 
of the class. We need not then examine all the members of the class in order 
to know what its properties are. Type study is a substitute for perfect 
induction, and while it has serious limitations, its advantages are very great 
for the economy of effort. The great extension of knowledge in every direc- 
tion has necessitated a development of some method of using it. Otherwise 
it becomes unwieldy and a student is overwhelmed by its very profusion. 
Type study is the method by which this great wealth of knowledge can be 
acquired and made available for service. The idea of a group that will 
include the various individuals studied is obtained by comparison of their 
properties, and selecting from the entire number those in which the indi- 
viduals agree. The concept of the more comprehensive group is obtained by 
observing the resemblances that exist among the types of the less compre- 
hensive groups. This process is called generalization, and is of essential 
importance. In fact, most of the other operations of the mind may be 
regarded as tributary to this one function. It necessitates a good many 
preliminary operations; abstraction, analysis, discrimination and comparison 
always precede. 
The perception of resemblances is a more difficult process and a higher 
order of thought than is the perception of differences. There are acute minds 
that have in a marked degree the power to see differences, but whose ability 
to see resemblances is exceedingly limited. In order to generalize, we must 
often see a logical identity existing in objects that on first examination appear 
to be wholly unlike. Paradoxes are fused into a unity, and things that seem 
to be so diverse as to render an assertion of their identity absurd, are seen 
to be essentially the same. 
Every mind must generalize, and every mind has the power so to do. but 
the differences in this power, in different individuals are very great. It Is 
a power that can be exercised safely only with much caution and after long 
training. Every great advance in thought has followed a wider and more far- 
reaching generalization. Those who are capable of making such generaliza- 
tions are the philosophers and leaders of thought. In natural science we 
are taught consciously how generalizations are made, and the necessary cau- 
tions to be employed. Science than, is the great training ground of those 
who generalize, and from the ranks of scientific men, or those trained in 
scientific methods, the philosophers of the future are sure to come. 
In the collection of material, the mind becomes buried under a mass of 
details. We must select out of this mass of material particular things that 
