274 THE FACTORIAL HYPOTHESIS 
It is a matter of little theoretical importance what 
system of symbols is adopted, unless that system 
proves to be impracticable, or unless it implies re- 
lations that are unnecessary or unjustifiable. (See 
Appendix.) ; 
We do not wish to appear to base our objection to 
the presence and absence hypothesis on the im- 
practicability of its nomenclature in a new field, 
but rather on the grounds that the conception of 
presence and absence assumes that we do know 
something about the relation between character 
and factor that we can not possibly know. To as- 
sume the absence of a factor from the absence of a 
character is, in a sense, as naive as it was to assume 
that an animal moved toward light because it liked 
the light. 
It need not be denied that losses of factors may 
occur, and it may even be probable that a loss in the 
germ plasm might lead to a loss in some part or parts 
of the body, but there still remains no justification 
for the assumption in any given case that we can 
infer from the lack of a character in an animal or 
plant a loss of factors. Such an assumption is en- 
tirely gratuitous; and gives a totally false impression 
concerning the factorial hypothesis of Mendelian 
heredity. Moreover, if taken literally it may lead 
to unwarranted conclusions in other fields. 
It is similarly naive to assume the absence of a 
factor from the recessiveness of the character, yet 
the literature abounds with instances where the re- 
cessiveness of the character is taken as a criterion for 
