Jerry Everard's Introduction to Lacan ...
Lacan (1901-1980) - the years are important because of the context in which
Lacan was interested in how people became subjects - the self-conscious, speaking, signifying, cultural person that they wind up becoming with the acquisition of language.
Observing children both before and after language acquisition, Lacan came to the view that one important stage in the child entering culture and language is what he called the "mirror stage". The mirror stage is where the child begins to recognise its own image in the mirror - as an image. For this to occur, the child must recognise that the image is of itself, but also that the image is not itself (because it is a reflection). At this stage the child makes (or recognises) that s/he is a separate entity from the world. That is, the child recognises the world (the other image) as Other to its Self.
To signal that distinction - the gap between Self and Other - the child signifies that difference through the use of a sign. At this point the child has entered the symbolic order - language. The formation of a notion of self (the ego) is thus intrinsically tied up with the operation of language.
To digress for the space of a paragraph, it can be useful to note that the child does not enter language in a vacuum. S/he enters language within a language community - a social world - in which meanings are already in circulation. The modalities of this language community will inscribe the child within a social context - including gender, ethnicity, nationalism etc.
From this it follows that language and symbolic (or cultural) elements are central to the formation of the sense of self (the ego). This is a large shift from the previously held view that human subjectivity was based on biological factors. (some feminist theorists seek to reinstate the biological in the constitution of gender as an aspect of subjectivity).
Back to Lacan. The Swiss linguist, Ferdinand de Saussure, noted back in his Course in General Linguistics (1911) that the relationship between the signifier and the signified is arbitrary (for example the relationship between the word "tree" and the idea of a tree is arbitrary, because the idea of tree can be signified by other sounds, such as "Arbre").
This was coupled with the view of language as a system of differences - whereby meaning is construed in negative terms (not this or not that). Because the sign stands in place of, and is not the THING itself (like the reflection IS not the child) access to the signified is always displaced, put off until later (this is Derrida's differance - different and deferred). So too the subject is never complete - always sliding from one signifier to the next in a never-ending succession of signifiers - never quite resting on a signified.
These insights led Lacan to the view that the subject is the subject of the process of signification. In this view the realm of the signifier is the realm of the Symbolic order - the order of signs, symbols, representations and images of all kinds (not merely words). In this order the individual is formed as subject.
I like to put it in terms of the subject being produced as a symptom
of the processes of signification in which the individual is embedded/inscribed.
Lacan said many other things as well, but I think his theory of subjectivity is one of the most important.
I have found two papers in his ECRITS well worth close study. These are: 'The Agency of the Letter in the Unconscious or Reason Since Freud' and The Mirror stage as Formative of the Function of the I'.
One of the best short introductions to Lacan is the Lacan section in John Lechte 'Fifty Key Contemporary Thinkers from Structuralism to Postmodernity' published by Routledge 1994