The Macmillan standard library

An Irish bull is a ludicrous, incongruent or logically absurd statement, generally unrecognized as such by its author. The inclusion of the epithet Irish is a late addition. John Pentland Mahaffy, Provost of Trinity College, Dublin, observed, "an Irish bull is always pregnant", i.e. with truthful meaning. The "father" of the Irish bull is often said to be Sir Boyle Roche, who once asked "Why should we put ourselves out of our way to do anything for posterity, for what has posterity ever done for us?".