Husserl, known as the father of the Phenomenology movement, sought to describe human experiences and Kantian “things in themselves” without making metaphysical assumptions. That is, he attempts to describe phenomenon in terms of how they appear in his own consciousness without conflating with the naturalistic and other scientific attitudes of his times. In contrast with scientific naturalism that use induction and general theories to organize large collections of data, phenomenology investigates particular examples of one’s own consciousness to discern what is essential to such experiences. i.e. to construct a theory of science that would ground all other sciences (much like psychology).
To systematize human experience into a theory of science, Husserl begins with language (propositional systems) as units of consciousness; the consciousness that gives voice to language are so-called “intentional acts” or “intentional experiences” that representing something as something. Such acts may be about non-existing (imagined, phantasy content) objects which includes forms of mental imagery (pictoral and kinesthetic representations). These acts differ from non-intentional units such as affects, moods, senses (pain) that are non-representational (not about anything).
The structure of consciousness could be partitioned into the act of consciousness and the phenomenon that it is being directed at. To arrive at knowledge of essences or “objects in themselves that appear in consciousness” he introduces a method called “bracketing” (Epoche) which culls away assumptions of how we normally think of objects as separate, external things. What we are left with are the invariant features that are perceived which constitute our understanding of the object. For example, my understanding of a rectangle can be bracketed to yield a four-sided shape with four right-angles. Abstract species such as rectangles of same area can be eidetically reduced to shapes of rectangles whose product of lengths and widths are the same. Such common features are said to have consistent meanings that are fulfilled by a “unified intuition” which can be read-off.
For indexical or context-sensitive experiences, Husserl characterizes them by their “singularity”, i.e. the object or set of intentional objects that are relevant in all possible worlds. The indexical experience is thought of as one of many worlds on a manifold that pertain to future courses of experiences with the indexical case as its root. These potential experiences constitute the “intentional horizon” conditioned on the indexical event. e.g. the anticipation of a moving car. Experiences on such a horizon share a common identity labeled as “determinable” X which is a higher-order (moment) belief/judgment.
For inter-subjectivity, we undergo acts of empathic experience where conscious acts are attributed to other subjects. The existence of other subjects follows from an egocentric view that others who act in ways similar to my own will perceive things in ways similar to my own; one puts himself in the other’s shoes. Such a belief allows one to ascribe intentional acts to others without inference (self-evident) and is a part of the intentional background or “lifeworld” or foundation of sense-making that is built into language and culture a priori. Lifeworld is thus a “world-horizon” of all potential experiences. e.g. prescientific qualities such as spatial shape, motion, body, and spatiotemporality. These qualities ground the more objective sciences when they employ any propositional content or appeal to intuitive acceptance (self-evident truths).
Heidegger sought to peer behind Western metaphysics by engaging in the pre-theoretical conditions necessary for intentionality (representations of things) in human thought. That is, what does “to exist” or “to be” mean with regards to entities (beings); Heidegger refers to what makes beings intelligible (able to be represented) as the meaning of Being (not in the set of being). This ontological difference between being and Being (as not a super-being) is conflated in the story of Western philosophy since the time of Plato which equated the meaning of Being to a series of beings (namely idea, substance, monad, subjectivity, and will-to-power). Such a distinction is relevant as all categories of thought that do not clarify the ontological difference are subject to the limits of their mode of Being. Thus, the investigation of the a priori transcendental conditions for modes of Being is Heidegger’s preoccupation.
Heidegger begins with the the unique mode of Being for humans (Dasein) as “the having-to-be-open” or “Being is an issue for it”. This is to say that Dasein tends towards sense/meaning-making, to make intelligible. The phenomenological method for examining such tendencies is hermeneutic (interpretive) and historically embedded. Dasein begins with ordinary encounters with entities (equipment) through the their skillful use (readiness-to-hand). While engaged in the activity, Dasein lacks a conscious awareness of the equipment as an independent entity in the way that one would if standing back; the person is absorbed in the world with the equipment and so the person has no awareness of himself as a subject separate from a world of objects. This mode of encountering contrasts with scientific and philosophical activity where the senses are means to reflection and contemplation of context-free entities (present-at-hand). The transitory phase between these two modes of being refers to an un-readiness-to-hand where skilled activity is disturbed but remain phenomenologically near in context; a piece of broken equipment may still be adapted for use. Dasein is in (dwells) the world of beings in the ways that equipment are involved; the network of intelligibility or relational ontology is the totality of involvements with teleological “for-the-sake-of-which” ends; involvements are choices towards that end during which entities are made intelligible. Dasein’s place in the world of involvements is thus spatial in the sense of readiness-to-hand; entities are nearby if they are readily available for activity and far away if not irregardless of physical distance. The who of Dasein in this world is to be-with entities that can be encountered by the Other; what Dasein do is determined by “what one does” which is historically and culturally conditioned.
Dasein’s relation with the world can also be interpreted as “care” through the dynamics of “thrownness, projection, and fallen-ness” for unpacking “having-to-be-open” and temporality. Thrownness or having been thrown into the world is Dasein’s confrontation with the set of historically conditioned possibilities for acting (past). Dasein understands each possibility by projecting itself onto each possibility (future) according to its network of totalities. The realization of understanding is through skilled read-to-hand encounters (present). Fallen-ness is the loss of Being its Self (making things intelligible) through everydayness of the they (idle talk, search for novelty, and ambiguity). Thus, the authentic self seeks to find its own relation to other entities rather than be lost to the they. To discover such relations, Daesin can use the possibility of its own death (“possibility of the impossibility of any existence at all”) to disclose the negation of all its relation and so conversely discloses them. The authentic relation to death is one of anticipation rather than expectation where the latter is a fear (passive) that discloses only some beings in the world; the former “owns death” by using its possibility to affirm new relations and modes of Being.
Heidegger’s later works (after the turn) shifts Dasein’s mode of Being from temporality to that of dwelling; the subjectivity of Being from Dasein’s relation is abandoned in favor of the historical account of the unfolding of Being. The history of Being is now represented as transformations that have shaped Dasein’s intelligibility; human beings dwell between the earth and sky (nature) and before mortals and divinities (culture). The relationship with nature is poetic habitation rather than scientific (instrumental), culture requires an openness towards death and the possibility of paradigm shifts in intelligibility (new cultural templates). The latter is most relevant to the modern age of technological thinking where things are intelligible according to being enframed or “challenged” in order to produce something to be held in “standing-reserve” for use. Technology’s clearing (when things are revealed as mattering in some way) turns nature into resources to be extracted, stored, and ultimately exploited as a means to an end. The issue of technological thinking is its domination and the consequent forgetfulness of Being; enframing covers up the fact that technology is only one mode of making things matter, a single clearing rather than one of many possible modes of revealing (poiesis). Ultimately, Heidegger’s solution to realizing poiesis was through artisanship, attentive listening (tuning with rhythms of nature), and adopting a non-evasive attitude towards death.