These are my principles. If you don’t like them I have others.
Was Groucho impersonating a politician when he said this?
QI: It is not clear if Groucho ever did say this quotation. But your belief that it is associated with politicians does have strong evidentiary support. In fact, the joke has a long history, and a version was being told before Groucho was born. The connection with politicians goes back more then one hundred years.
The marvelous compendium, the Yale Book of Quotations, has examined the quote and found an attribution to Groucho in 1983 in Legal Times. This is a suspiciously late date since Groucho died in 1977.
QI found this version of the quip in a New Zealand paper dated October 18, 1873 [NZT]:
He brought in the Provincial Loan Bill, declaring that, if the House did not accept it, he was prepared to adhere to his original proposal. It was something like the American legislator — “Them’s my principles; but if you don’t like them — I kin change them!”
The joke appeared again in New Zealand on August 18, 1878 [GREY]:
The American candidate had a very good estimate of the best way to command popular support when, after having described such manufactured principles as he had got ready, said – “Them feller citizens are my principles, but if they don’t suit yer exactly, they ken be altered.”
In 1899 the joke is told in Canada about a “great American stump orator” [CN]:
These, gentlemen, are my principles, but if you do not like them I can change them.
Skipping forward to 1975, a Canadian politician named Darcy McKeough is criticized for employing the joke as a humorous excuse for possible future changes in policy. The wording used is similar to that in the version attributed to Groucho [MCK]:
“You’ve all heard,” he (Darcy McKeough) told the locked-up press, “of the politician who wound up his speech saying: ‘ladies and gentlemen, those are my principles, and if you don’t like them I have some others.’ If events I can’t foresee alter the basis of this budget and undermine its effectiveness, I’ll have no hesitation about coming back to it later in the fiscal year.”
It is possible that Groucho or one of his writers heard the joke and then Groucho used it in a radio show, TV show, or other performance. He also may have used it in an interview or a letter, but the earliest citation establishing a connection that is currently known to QI is the one in the Yale Book of Quotations.
[NZT] 1873 October 18, New Zealand Tablet, Weekly Epitome, Page 7, Column 2, Volume I, Issue 25, New Zealand. (Google News Archive, National Library of NZ, Papers Past) link
[GREY] 1878 August 18, The Grey River Argus, Published Daily, Page 2, Column 2, Volume 21, Issue 3123, New Zealand. (Google News Archive, National Library of NZ, Papers Past) link
[CN] 1899 February 17, Daily Mail And Empire, Great Meeting at Goderich, Page 2, Column 4, Toronto, Canada. (Google News Archive) link
[MCK] 1975 April 14, The (Ottawa) Citizen, Temporary Budget by Harold Greer, Page 6, Ottawa, Canada. (Google News Archive) link