“How many legs does a dog have, if you call a tail a leg?”
His collected works contain no riddle about dog legs, but George W. Julian recounts Lincoln using a similar story about a calf in Reminiscences of Abraham Lincoln by distinguished men of his time (1909), p. 241: "There are strong reasons for saying that he doubted his right to emancipate under the war power, and he doubtless meant what he said when he compared an Executive order to that effect to 'the Pope’s Bull against the comet.' In discussing the question, he used to liken the case to that of the boy who, when asked how many legs his calf would have if he called its tail a leg, replied, 'Five,' to which the prompt response was made that calling the tail a leg would not make it a leg."
A very similar riddle about cow legs was also circulated by Edward Josiah Stearns' Notes on Uncle Tom's Cabin (1853), p. 46: '"Father," said one of the rising generation to his paternal progenitor, "if I should call this cow's tail a leg, how many legs would she have?" "Why five, to be sure." "Why, no, father; would calling it a leg make it one?"'
Misattributed
Help us to complete the source, original and additional information
Abraham Lincoln 618
16th President of the United States 1809–1865Related quotes

The Notebooks of Leonardo Da Vinci (1938), XVII Flight

"The Wrestler"
Song lyrics, Working on a Dream (2009)

“Listen to the Chair Leg of Truth! It does not lie!”
Source: Transmetropolitan, Vol. 9: The Cure

“Does a one-legged duck swim in circles?”
"This is the week that...", The Times, 5 December 1998, p. 8.
Reply to Jeremy Paxman on BBC Newsnight when asked whether he still wanted to lead the Labour Party in the National Assembly for Wales.
Morgan was awarded the "Foot in Mouth" award by the Plain English Campaign on 11 December 1998 for this quote.

July 31, 1763, p. 132. [Several editions have the variant "hind legs".]
Life of Samuel Johnson (1791), Vol I

The Music Grinders; reported in Bartlett's Familiar Quotations, 10th ed. (1919).