rationale

*****************************************************************
Discover the people and events that made history ON THIS DAY. 
Sign up for the free daily newsletter from Britannica.
http://register.britannica.com/mailinglist
*****************************************************************

The Word of the Day for December 12 is:

rationale   \rash-uh-NAL\   noun 
     1 : an explanation of controlling principles of opinion, 
belief, practice, or phenomena 
    *2 : an underlying reason : basis 

Example sentence: 
     One rationale for year-round school is that it reduces the 
need to review old material forgotten over summer vacation.

Did you know? 
     The word "rationale" appeared in the second half of the 
17th century, just in time for the Age of Reason. It is based on 
the Latin "ratio," which means "reason," and "rationalis," which 
means "endowed with reason." At first, "rationale" meant "an 
explanation of controlling principles" ("a rationale of 
religious practices," for example), but soon it began to refer 
to the underlying reason for something (as in "the rationale for 
her behavior"). The latter meaning is now the most common use of 
the term. The English word "ratio" can also mean "underlying 
reason" (in fact, it had this meaning before "rationale" did), 
but in current use, it more often refers to the relationship (in 
number, quantity, or degree) between things. 

*Indicates the sense illustrated in the example sentence.