It seems that Keynes was the one who first _insisted_ on having Y for 
Yncome. I believe he put it that way in one of his earlier manuscripts. = 
He 
uses this notation through all of the _General Theory_. Right now I have 
only Vol XIV of Keynes' Collected Writings with me. There (JMK, CW, XIV, 
p.80) Keynes writes to Hicks (in response to his SILL-article which = 
intends 
to render the essence of the General Theory): "On one point of detail, I 
regret that you use the symbol _I_ for income. ... after trying both, I 
believe it is easier to use _Y_ for income and _I_ for investment. = 
Anyhow we 
ought to try and keep uniform in usage."  
 
There you have _Y_ as notational programme. To this Hicks was to reply = 
(JMK, 
CW, p.81):  
 
"I am sorry about using _I_ for income. ... I hadn't the ghost of an = 
idea 
... that there was any particular sanctity about _Y_, and that it hadn't 
just been drawn out of a hat."  
 
 
Therefore I conclude that it was Keynes' _General Theory_ which started = 
the 
convention of Y =3D income. 
 
Michael Ambrosi