In philology, a lapsus (Latin for "lapse, slip, error") is an involuntary mistake made while writing or speaking.

In 1895 an investigation into verbal slips was undertaken by a philologist and a psychologist, Rudolf Meringer and Karl Mayer, who collected many examples and divided them into separate types.

Freud was to become interested in such mistakes from 1897 onwards, developing an interpretation of slips in terms of their unconscious meaning. Subsequently, followers of his like Ernest Jones developed the theme of lapsus in connection with writing, typing, and misprints.

According to Freud's early psychoanalytic theory, a lapsus represents a bungled act that hides an unconscious desire: “the phenomena can be traced back to incompletely suppressed psychical material...pushed away by consciousness”.

Jacques Lacan would thoroughly endorse the Freudian interpretation of unconscious motivation in the slip, arguing that “in the lapsus it is...clear that every unsuccessful act is a successful, not to say 'well-turned', discourse”.

In the seventies Sebastiano Timpanaro would controversially take up the question again, by offering a mechanistic explanation of all such slips, in opposition to Freud's theories.

In literature, a number of different types of lapsus are named depending on context:

Slips of the tongue can happen on any level: