According to the theory, a similar conflict could be found in dreams. But dreams were so complex and significant, based as they were on experiences of early life, that they needed expert advice to unravel. This is why generations of Freudian analysts whose business it has been to do the unravelling have prospered.
Freudian slips by comparison are plain man's stuff, allowing everyone to be their own psychologist. When Radio 4's Today referred recently to the BBC'S "new spanking building" instead of "spanking new building", listeners responded to the unconscious innuendo with gleeful letters.
The central text is The Psychopathology of Everyday Life, subtitled "Forgetting, Slips of the Tongue, Bungled Actions, Superstitions and Errors", first published in book form in 1904 and then enlarged, edition by edition, over the next 20 years. The forgetting of names fills pages, the general idea being that the forbidden word has distressing or annoying associations that are best covered up. Freud, who had a sense of humour, even suggested that aristocrats have difficulty remembering the names of doctors they consult because inwardly they despise them. On the action front, people may be punishing themselves. Thus men who look back lustfully at women in the street often sprain an ankle or walk into a lamppost. One has to assume this happened more often in Freud's time than it does in ours.
Sex was often lurking. Freud quotes a colleague, a womaniser called Stekel, who entered a house, put out a hand to greet his hostess and "contrived in doing so to undo the bow that held her loose morning-gown together. I was conscious of no dishonourable intention; yet I carried out this clumsy movement with the dexterity of a conjurer."
A wife who complained that her husband made too many sexual demands - as wives seemed to, in those days - found him using her face-powder on his chin after shaving, and said, "There you go again, powdering me with your puff." By reversing what she meant to say, "powdering yourself with my puff", she produced an unconscious sexual rebuke, "powdering" being Viennese slang for copulating, while "puff" was doubtless a phallic symbol.
As early as 1914, when the book first appeared in an English translation, a popular magazine in London was telling readers about this "curious and fascinating new system of self-examination", which is about the level of significance that most of us still grant it. The deeper message - that if a "Freudian slip" suggests anything, it is that we are never as fully in control of ourselves as we like to think - is overlooked.
Freud's obsessive, ambitious nature made him take all his beliefs to extreme lengths, which is not to deny the grains of truth scattered thickly through his books.
I like to think I found an unacknowledged example by Freud, about Freud, where, in another work, he described getting lost in a town and finding himself three times in the same street of brothels. Internal evidence suggests that he was remembering an episode in Trieste when he was a young man. However, he ignored the obvious conclusion, that the reason he kept returning was his hidden desire to visit a prostitute.
Watching for others' Freudian slips is an amusing game, but be careful they aren't watching for yours.
Paul Ferris is the author of `Dr Freud: a life' (Pimlico, pounds 15)