How we change what others think, feel, believe and do
This is the view of identity being built by being the 'subject' of language.
There is a whole position around identity as being the 'subject of language' that takes an anti-humanist and structural view of the person. 'Humanity' is ignored in favor of the way our environment and cultures controls us through language, replacing the purposeful agent with a dumb puppet.
Althusser's 'subject' came from attempts to rethink Marxism, using structuralism in opposition to mechanistic thought in a more humanist way, seeking to put conscious activity at the heart of Marxism in combination with the 'alienation' of people from their full altruistic potential.
He saw human individuals being constituted as subjects through ideology. Consciousness and agency are experienced, but are the products of ideology 'speaking through' the subject.
Althusser uses Lacan's mirror phase to highlight how subjects are interpellated, but does not recognize the critical misrecognition that Lacan highlights. Althusser has also been criticized for how his subject is magically created of nowhere (what is there before the subject?).
For Saussure, the subject is an effect or product of the process of signifying. He believed that nothing exists outside of language, including 'I'.
Benveniste said that man constitutes himself as a subject in and through language, and that 'ego is he who says "ego"'. This challenges the notion that 'I' exists outside of language. Speaking from 'I' creates the 'I'. 'I' can also be used (by you) to mean you, making it unstable as a definer of identity. Identity (as everything) in language comes from difference. To define 'I' there must be a 'you'. These are also reversible, as 'I' become 'you' when others talk.
Barthes noted that language knows a subject, but not a person.
Lacan argues that subject positions are made available in the symbolic order into which people place themselves in order to speak that position. He also noted that there is always a gap between the subject and the subject position they inhabit.
Hall notes how the speaker and the spoken are never identical, thus fragmenting identity across time and space.
In grammar, the subject is the person or thing in a sentence that does what the verb says, to the object. Thus, in 'the cat sat on the mat', the cat is the subject and the mat is the object.