: We see two references now. One is from Paul Graham and neither an independenrt nor an authoritative source about the history of Algol respectively Lisp. The other, by John McCarthy, even refutes the claim: I invented conditional expressions in connection with a set of chess legal move routines I wrote in FORTRAN for the IBM 704 at M.I.T. during 1957-58. This program did not use list processing. The IF statement provided in FORTRAN 1 and FORTRAN 2 was very awkward to use [...] This led to the invention of the true conditional expression which evaluates only one of N1 and N2 according to whether M is true or false and to a desire for a programming language that would allow its use. A paper defining conditional expressions and proposing their use in Algol was sent to the Communications of the ACM but was arbitrarily demoted to a letter to the editor, because it was very short. For one, it does not say If/Then/Else here, as claimed. Secondly, the development began in a Fortran context and it has been passed on directly to Algol58. So, Algol cannot have it from Lisp.