The way out of this metonymical chain of unsatisfied desire, for Lacan, is a "crossing of the bar" by a signifier: Lacan emphasises 'the constitutive value of this crossing for the emergence of signification'. Lacan aligns this operation with metaphor rather than metonymy. When a signifier crosses the bar, from above it to under it, it becomes a signified. But this leaves a space or gap above the bar which, according to Lacan, is the subject. In Lacanian psychoanalysis, the subject only appears fleetingly, on those rare occasions when a signifier crosses the bar, leaving an empty space above it.