In the 17th Century, British Empiricists took “the world” to be little more than a series of sense perceptions, perhaps perceptions of something – but we would never know. The Cartesian subject, the "I" of the "I think", sits apart from the world, receiving it. Berkeley went so far as to say “to be is to be perceived” (esse est percipi). Their fundamental insight seems correct: my view of the world is determined merely by a series of sense perceptions; if I encounter an illusion (a stick bent in some water, for example) I only know it is an illusion because of some later experiences which contradict the earlier ones.
If one adopts this frame-by-frame view of experience, many things go out the window: from causation to scientific (inductive) knowledge itself. For example, in a recording of a pool game we see the balls moving after being struck by a cue: however the patch of light (“cue”) moving across the screen does not cause the other patch of light (“ball”) to move: it only appears this way (and there is nothing to suggest it couldn't happen some other way in the future). The apparent coordination, according to Berkeley is provided by God: God’s mind is thus the transcendental director coordinating all of our cameras.
British Empiricism is therefore a kind of scepticism which reduces the world to atoms of sense perception, and in some cases, with no coordinating force. In the empiricist Humean vision causation is a habit: we get used to one thing following another, and so we say it causes it. However, does it really take a repetition to infer causation? We only need to burn our hands once to be weary of trying again. It seems that causation is already baked into experience in a way which associates events spontaneously. We thus have to transition to Kantian metaphysics to incorporate this insight.
Kant’s replies to the empiricists is an effort to preserve knowledge and science. In Kantian metaphysics we admit a fundamental division between things-in-themselves, the foundational material of the world (noumena) and the way things appear (phenomena), and then introduce a transcendental subject to perform the work of coordination: whilst this “subject” is formally a mind, it is little above the various harmonizing processes it engages in. These processes (or faculties) “make sense” of the world: they are responsible for causation, space, time and other features which arise out of a noticeable consistency across experience.
The transcendental subject exists in relation to the Cartesian “I”. It is the case that when I say “I see” I can be speaking about something which is objective (eg. a tree) or subjective (eg. a memory of a tree), and so the “I” of myself can “take things objectively”: I can switch between “being in the film” and seeing the film from the camera’s point-of-view.
Fichte looked at this system and puzzled. If we are having a series of phenomenal experience which are fundamentally separated from the noumena, and if all the consistencies of experience are provided by the transcendental subject: what exactly is the noumena doing? Fichte thus removed the noumenal from the equation entirely. We then move to something closer to a secularization of Berkeley’s programme into which Hegel steps, taking Fichtean metaphysics as a universal system for explaining the world, and imbuing the transcendental subject (or “Spirit”) with a logic and structure. The Hegelian world evolves according to this logic (the dialectic), which synthesizes (sublates) contradictory social and historical forces into a progression, so that each future moment incorporates and improves upon the last.
Marx recognized these dialectical forces in the operation of society and history, but was weary of the metaphysics which underpinned them. In his “historical” materialism, we leap back to the alternative stream woven through British Empiricism: that sense perceptions derive from a material world. Marx wants to imbue this world with the forces of its own organization so as to bake into the materiality of things, their own self-directing structure. Thus Marx reduces the Hegelian transcendental subject to a fully material consequence of how the natural forces of the world work. What though, for the other side of the subject? If the camera is reducible to material forces, is then the “I” of “I see” also merely a product of historical forces: yes.
Freud (and possibly Nietzsche) enters here and fleshes out this new material subject: it is still composite, but now made from an underlying inaccessible unconscious and a coordinating rationalizing consciousness. Across these two inner-worlds span the superstructures of the coordinating forces (transcendental, social and historical) that Marx and Hegel noticed. The subject, in relation to other subjects, and to the world, internalizes society and “civilizes” itself against a background of turbulent inner psychological world. This composite subject is then not a unified person with a “rational self-interest” and inquiring nature but rather many contradictory and competing forces: a superego which makes impossible moral demands, an id of basic drives and an ego which tries to make sense of it all.
Materialism however, in the 19th Century and turn of the 20th wasn't the predominant metaphysics, rather this goes to British and German idealism. It is this metaphysical milieu that the next generation of philosophers rejected: Carnap, Husserl, Russell, Heidegger, etc. Both Carnap and Husserl turned towards consciousness as a certain bedrock on which to found a new science of philosophical investigation. In the Husserlian case we return to a systematized Fichtean system but without the Kantian trappings: consciousness is the unified foundational “world” from which all claims, knowledge and science is derived. We must therefore formally bracket (put aside) questions of what “underpins” consciousness, if anything, and turn towards a direct and systematic investigation of consciousness itself. It is with this gesture Husserl invents phenomenology.
In Husserl’s phenomenological system we retain a neo-Kantian “transcendental ego” a unifying, organizing aspect of the subject. It is to this both Satre and Heidegger react. For Heidegger the world is not like a large surface over which the transcendental ego hovers, but a real and dark expanse which is partially illuminated by the subject (which he calls Dasein), and in this area of illumination (clearing), the world “shows itself” to the subject in its various modes of existence. Sartre, following Heidegger, also moves into a more realist phenomenology noting that the transcendental ego is formally a view from nowhere: that it is not present within the phenomenal itself, and thus by Husserl’s own method, ruled out. We are then left with a perplexing realist phenomenology: a “world” which is neither material nor ideal, and in which subjects are embedded as ontologizing forces.
From one view, that of Levinas, this position is a hair’s breadth from a fully social (subject-ive) ontology (a social constructivism, perhaps). And so we enter a radically new metaphysical space which rejects materialism, idealism, the Hedieggerian and the Husserlian. Subjects, and their relation to one another, constitute the world. Into this, via Althusser, Lacan and Freud are co-opted phenomenologizing their clinical (contra philosophical) projects.
For Althusser the “I” is a spontaneous construction of ideology, deriving from the Lacanian analysis of the subject. Lacan adds language to Freud, making the psychological processes of the subject fundamentally linguistic processes. Ideology is the superstructure of this social metaphysics out of which subjects emerge, their identities and their constitution. This is effectively a neo-Hegelian system in which society and the world are subject to forces driven by a transcendental subject, but without the transcendental subject. A world coordinated by Freudian composite subjects, structured by linguistic processes rather than the material ones.
Within Lacan however there is a Real, and within Freud there is the material. And so the unstable metaphysics of this era settles into a new “transcendental materialism” which coalesces in the work of Slavoj Zizek. In this metaphysical system Hegel, Marx, Freud, Lacan are united. The material word, as in the Marxian system, contains its own motive-forces but this world is not the mechanistic realist vision of “billiard balls colliding” but rather closer to the realist phenomenology of Heidegger. In this system we finally get an account of a material transcendental: how it can be that from a material world there can emerge large coordinating forces. The site of the transcendental, in this system, is within subjects: but not the hollow Humean pin-hole subjects which receive sense perceptions. Subjects which are generated from a union between the material and the social. In the social we have the Althusserian-Lacanian linguistic superstructures and the material we have the empirical bodies. And so the moment the subject comes into being, so does the transcendental: essentially a sophisticated “constructive materialism” wherein the constructive processes are provided by Hegel and Lacan and the material processes by Marx.
So today, the subject, is the site of the amalgamation of this history of continental metaphysics: in some way incorporating the thoughts of every major philosopher since Kant.