(The), subs. phr. (colloquial).The reason, cause.
1593. SHAKESPEARE, Comedy of Errors, ii. 2. Every WHY hath a WHEREFORE.
1624. FLETCHER, Rule a Wife and Have a Wife, iii. 1. Dispute learnedly the WHYS AND WHEREFORES.
1809. MALKIN, Gil Blas [ROUTLEDGE], 373. When I let him into the WHY AND the WHEREFORE, he laughed ready to split his sides.
d. 1897. JEAN INGELOW, Not in Vain I Wanted. The WHY AND THE WHEREFORE of it all who knoweth?