Phenomenology (from Greek: phainómenon "that which appears"; and lógos "study") is a philosophical movement. It was founded in the early years of the 20th century by Edmund Husserl, expanded together with a circle of his followers at the universities of Göttingen and Munich in Germany, and spread across to France, the United States, and elsewhere, often in contexts far removed from Husserl's early work.
Phenomenology, in Husserl's conception, is primarily concerned with the systematic reflection on and analysis of the structures of consciousness, and the phenomena which appear in acts of consciousness. Such reflection was to take place from a highly modified "first person" viewpoint, studying phenomena not as they appear to "my" consciousness, but to any consciousness whatsoever. Husserl believed that phenomenology could thus provide a firm basis for all human knowledge, including scientific knowledge, and could establish philosophy as a "rigorous science".
Husserl's conception of phenomenology has been criticised and developed not only by himself, but also by his students Edith Stein and Martin Heidegger, by existentialists, such as Max Scheler, Nicolai Hartmann, Maurice Merleau-Ponty, Jean-Paul Sartre, and by other philosophers, such as Paul Ricoeur, Emmanuel Levinas, and Alfred Schütz.
In its most basic form, phenomenology attempts to create conditions for the objective study of topics usually regarded as subjective: consciousness and the content of conscious experiences such as judgments, perceptions, and emotions. Although phenomenology seeks to be scientific, it does not attempt to study consciousness from the perspective of clinical psychology or neurology. Instead, it seeks through systematic reflection to determine the essential properties and structures of consciousness and conscious experience.
Husserl derived many important concepts central to phenomenology from the works and lectures of his teachers, the philosophers and psychologists Franz Brentano and Carl Stumpf. An important element of phenomenology that Husserl borrowed from Brentano was intentionality (often described as "aboutness"), the notion that consciousness is always consciousness of something. The object of consciousness is called the intentional object, and this object is constituted for consciousness in many different ways, through for instance perception, memory, retention and protention, signification, etc. Throughout these different intentionalities, though they have different structures and different ways of being "about" the object, an object is still constituted as the same identical object; consciousness is directed at the same intentional object in direct perception as it is in the immediately following retention of this object and the eventual remembering of it.
Though many of the phenomenological methods involve various reductions, phenomenology is essentially anti-reductionistic; the reductions are mere tools to better understand and describe the workings of consciousness, not to reduce any phenomenon to these descriptions. In other words, when a reference is made to a thing's essence or idea, or when one details the constitution of an identical coherent thing by describing what one "really" sees as being only these sides and aspects, these surfaces, it does not mean that the thing is only and exclusively what is described here: The ultimate goal of these reductions is to understand how these different aspects are constituted into the actual thing as experienced by the person experiencing it. Phenomenology is a direct reaction to the psychologism and physicalism of Husserl's time.
Although previously employed by Hegel, it was Husserl’s adoption of this term (circa 1900) that propelled it into becoming the designation of a philosophical school. As a philosophical perspective, phenomenology is its method, though the specific meaning of the term varies according to how it is conceived by a given philosopher. As envisioned by Husserl, phenomenology is a method of philosophical inquiry that rejects the rationalist bias that has dominated Western thought since Plato in favor of a method of reflective attentiveness that discloses the individual’s “lived experience.” Loosely rooted in an epistemological device, with Sceptic roots, called epoché, Husserl’s method entails the suspension of judgment while relying on the intuitive grasp of knowledge, free of presuppositions and intellectualizing. Sometimes depicted as the “science of experience,” the phenomenological method is rooted in intentionality, Husserl’s theory of consciousness (developed from Brentano). Intentionality represents an alternative to the representational theory of consciousness which holds that reality cannot be grasped directly because it is available only through perceptions of reality which are representations of it in the mind. Husserl countered that consciousness is not “in” the mind but rather conscious of something other than itself (the intentional object), whether the object is a substance or a figment of imagination (i.e. the real processes associated with and underlying the figment). Hence the phenomenological method relies on the description of phenomena as they are given to consciousness, in their immediacy.
According to Maurice Natanson (1973, p. 63), “The radicality of the phenomenological method is both continuous and discontinuous with philosophy’s general effort to subject experience to fundamental, critical scrutiny: to take nothing for granted and to show the warranty for what we claim to know.”
In practice, it entails an unusual combination of discipline and detachment to suspend, or bracket, theoretical explanations and second-hand information while determining one's “naive” experience of the matter. The phenomenological method serves to momentarily erase the world of speculation by returning the subject to his or her primordial experience of the matter, whether the object of inquiry is a feeling, an idea, or a perception. According to Husserl the suspension of belief in what we ordinarily take for granted or infer by conjecture diminishes the power of what we customarily embrace as objective reality. According to Safranski (1998, 72), “[Husserl and his followers’] great ambition was to disregard anything that had until then been thought or said about consciousness or the world [while] on the lookout for a new way of letting the things [they investigated] approach them, without covering them up with what they already knew.”
Heidegger modified Husserl’s conception of phenomenology because of (what he perceived as) his subjectivist tendencies. Whereas Husserl conceived humans as having been constituted by states of consciousness, Heidegger countered that consciousness is peripheral to the primacy of one’s existence (i.e., the mode of being of Dasein) which cannot be reduced to one’s consciousness of it. From this angle, one’s state of mind is an “effect” rather than a determinant of existence, including those aspects of existence that one is not conscious of. By shifting the center of gravity from consciousness (psychology) to existence (ontology), Heidegger altered the subsequent direction of phenomenology, making it at once both personal and mysterious. One of the consequences of Heidegger’s modification of Husserl’s conception of phenomenology was its increased relevance to psychoanalysis. Whereas Husserl gave priority to a depiction of consciousness that was fundamentally alien to the psychoanalytic conception of the unconscious, Heidegger offered a way to conceptualize experience that could accommodate those aspects of one’s existence that lie on the periphery of sentient awareness.
Intentionality refers to the notion that consciousness is always consciousness of something. The word itself should not be confused with the "ordinary" use of the word intentional, but should rather be taken as playing on the etymological roots of the word. Originally, intention referred to a "stretching out" ("in tension," lat. intendere), and in this context it refers to consciousness "stretching out" towards its object. Intentionality is often summed up as "aboutness."
Whether this something that consciousness is about is in direct perception or in fantasy is inconsequential to the concept of intentionality itself; whatever consciousness is directed at, that is what consciousness is consciousness of. This means that the object of consciousness doesn't have to be a physical object apprehended in perception: it can just as well be a fantasy or a memory. Consequently, these "structures" of consciousness, i.e., perception, memory, fantasy, etc., are called intentionalities.
The cardinal principle of phenomenology, the term intentionality originated with the Scholastics in the medieval period and was resurrected by Brentano who in turn influenced Husserl’s conception of phenomenology, who refined the term and made it the cornerstone of his theory of consciousness. The meaning of the term is complex and depends entirely on how it is conceived by a given philosopher. The term should not be confused with “intention” or the psychoanalytic conception of unconscious “motive” or “gain.”
Intuition in phenomenology refers to those cases where the intentional object is directly present to the intentionality at play; if the intention is "filled" by the direct apprehension of the object, you have an intuited object. Having a cup of coffee in front of you, for instance, seeing it, feeling it, or even imagining it - these are all filled intentions, and the object is then intuited. The same goes for the apprehension of mathematical formulae or a number. If you do not have the object as referred to directly, the object is not intuited, but still intended, but then emptily. Examples of empty intentions can be signitive intentions - intentions that only imply or refer to their objects.
In everyday language, we use the word evidence to signify a special sort of relation between a state of affairs and a proposition: State A is evidence for the proposition "A is true." In phenomenology, however, the concept of evidence is meant to signify the "subjective achievement of truth."  This is not an attempt to reduce the objective sort of evidence to subjective "opinion," but rather an attempt to describe the structure of having something present in intuition with the addition of having it present as intelligible: "Evidence is the successful presentation of an intelligible object, the successful presentation of something whose truth becomes manifest in the evidencing itself." 
In Husserl's phenomenology, this pair of terms, derived from the Greek nous (mind), designate respectively the real content and the ideal content of an intentional act (an act of consciousness). The Noesis is the part of the act which gives it a particular sense or character (as in judging or perceiving something, loving or hating it, accepting or rejecting it, and so on). This is real in the sense that it is actually part of what takes place in the consciousness (or psyche) of the subject of the act. The Noesis is always correlated with a Noema; for Husserl the full Noema is a complex ideal structure comprising at least a noematic sense and a noematic core. The correct interpretation of what Husserl meant by the Noema has long been controversial, but the noematic sense is generally understood as the ideal meaning of the act and the noematic core as the act's referent or object as it is meant in the act. One element of controversy is whether this noematic object is the same as the actual object of the act (assuming it exists) or is some kind of ideal object.
In phenomenology, empathy refers to the experience of another human body as another subjectivity: In one sense, you see another body, but what you immediately perceive or experience is another subject. In Husserl's original account, this was done by a sort of apperception built on the experiences of your own lived-body. The lived body is your own body as experienced by yourself, as yourself. Your own body manifests itself to you mainly as your possibilities of acting in the world. It is what lets you reach out and grab something, for instance, but it also, and more importantly, allows for the possibility of changing your point of view. This helps you differentiate one thing from another by the experience of moving around it, seeing new aspects of it (often referred to as making the absent present and the present absent), and still retaining the notion that this is the same thing that you saw other aspects of just a moment ago (it is identical). Your body is also experienced as a duality, both as object (you can touch your own hand) and as your own subjectivity (you are being touched).
The experience of your own body as your own subjectivity is then applied to the experience of another's body, which, through apperception, is constituted as another subjectivity. You can thus recognise the Other's intentions, emotions, etc. This experience of empathy is important in the phenomenological account of intersubjectivity. In phenomenology, intersubjectivity is what constitutes objectivity (i.e., what you experience as objective is experienced as being intersubjectively available - available to all other subjects. This does not imply that objectivity is reduced to subjectivity nor does it imply a relativist position, cf. for instance intersubjective verifiability).
In the experience of intersubjectivity, one also experiences oneself as being a subject among other subjects, and one experiences oneself as existing objectively for these Others; one experiences oneself as the noema of Others' noeses, or as a subject in another's empathic experience. As such, one experiences oneself as objectively existing subjectivity. Intersubjectivity is also a part in the constitution of one's lifeworld, especially as "homeworld."
The lifeworld (German: Lebenswelt) is the "world" each one of us lives in. One could call it the "background" or "horizon" of all experience, and it is that on which each object stands out as itself (as different) and with the meaning it can only hold for us. The lifeworld is both personal and intersubjective (it is then called a "homeworld," and it is shared by "homecomrades"), and, as such, it does not enclose each one of us in a solus ipse.
In the first edition of the Logical Investigations, still under the influence of Brentano, Husserl describes his position as "descriptive psychology." Husserl analyzes the intentional structures of mental acts and how they are directed at both real and ideal objects. The first volume of the Logical Investigations, the Prolegomena to Pure Logic, begins with a devastating critique of psychologism, i.e., the attempt to subsume the a priori validity of the laws of logic under psychology. Husserl establishes a separate field for research in logic, philosophy, and phenomenology, independently from the empirical sciences.
Some years after the publication of the Logical Investigations, Husserl made some key elaborations which led him to the distinction between the act of consciousness (noesis) and the phenomena at which it is directed (the noemata).
What we observe is not the object as it is in itself, but how and inasmuch it is given in the intentional acts. Knowledge of essences would only be possible by "bracketing" all assumptions about the existence of an external world and the inessential (subjective) aspects of how the object is concretely given to us. This procedure Husserl called epoché.
Husserl in a later period concentrated more on the ideal, essential structures of consciousness. As he wanted to exclude any hypothesis on the existence of external objects, he introduced the method of phenomenological reduction to eliminate them. What was left over was the pure transcendental ego, as opposed to the concrete empirical ego. Now (transcendental) phenomenology is the study of the essential structures that are left in pure consciousness: this amounts in practice to the study of the noemata and the relations among them. The philosopher Theodor Adorno criticised Husserl's concept of phenomenological epistemology in his metacritique Against Epistemology, which is anti-foundationalist in its stance.
After Husserl's publication of the Ideen in 1913, many phenomenologists took a critical stance towards his new theories. Especially the members of the Munich group distanced themselves from his new transcendental phenomenology and preferred the earlier realist phenomenology of the first edition of the Logical Investigations.
Existential phenomenology differs from transcendental phenomenology by its rejection of the transcendental ego. Merleau-Ponty objects to the ego's transcendence of the world, which for Husserl leaves the world spread out and completely transparent before the conscious. Heidegger thinks of a conscious being as always already in the world. Transcendence is maintained in existential phenomenology to the extent that the method of phenomenology must take a presuppositionless starting point - transcending claims about the world arising from, for example, natural or scientific attitudes or theories of the ontological nature of the world.
While Husserl thought of philosophy as a scientific discipline that had to be founded on a phenomenology understood as epistemology, Heidegger held a radically different view. Heidegger himself states their differences this way:
According to Heidegger, philosophy was not at all a scientific discipline, but more fundamental than science itself. According to him science is only one way of knowing the world with no special access to truth. Furthermore, the scientific mindset itself is built on a much more "primordial" foundation of practical, everyday knowledge. Husserl was skeptical of this approach, which he regarded as quasi-mystical, and it contributed to the divergence in their thinking.
Instead of taking phenomenology as prima philosophia or a foundational discipline, Heidegger took it as a metaphysical ontology: "being is the proper and sole theme of philosophy... this means that philosophy is not a science of beings but of being.". Yet to confuse phenomenology and ontology is an obvious error. Phenomena are not the foundation or Ground of Being. Neither are they appearances, for as Heidegger argues in Being and Time, an appearance is "that which shows itself in something else," while a phenomenon is "that which shows itself in itself."
While for Husserl, in the epochè, being appeared only as a correlate of consciousness, for Heidegger being is the starting point. While for Husserl we would have to abstract from all concrete determinations of our empirical ego, to be able to turn to the field of pure consciousness, Heidegger claims that "the possibilities and destinies of philosophy are bound up with man's existence, and thus with temporality and with historicality."
However, ontological being and existential being are different categories, so Heidegger's conflation of these categories is, according to Husserl's view, the root of Heidegger's error. Husserl charged Heidegger with raising the question of ontology but failing to answer it, instead switching the topic to the Dasein, the only being for whom Being is an issue. That is neither ontology nor phenomenology, according to Husserl, but merely abstract anthropology. To clarify, perhaps, by abstract anthropology, as a non-existentialist searching for essences, Husserl rejected the existentialism implicit in Heidegger's distinction between being (sein) as things in reality and Being (Da-sein) as the encounter with being, as when being becomes present to us, that is, is unconcealed.
Existential phenomenologists include: Martin Heidegger (1889 – 1976), Hannah Arendt (1906 – 1975), Emmanuel Levinas (1906 – 1995), Gabriel Marcel (1889 – 1973), Jean-Paul Sartre (1905 – 1980), Paul Ricoeur (1913 - 2005) and Maurice Merleau-Ponty (1908 – 1961).
Some researchers in phenomenology (particularly in reference to Heidegger's legacy) see possibilities of establishing dialogues with traditions of thought outside of the so-called Western philosophy, particularly with respect to East-Asian thinking, and despite perceived differences between "Eastern" and "Western". Furthermore, it has been claimed that a number of elements within phenomenology (mainly Heidegger's thought) have some resonance with Eastern philosophical ideas, particularly with Zen Buddhism and Taoism. According to Tomonubu Imamichi, the concept of Dasein was inspired — although Heidegger remains silent on this — by Okakura Kakuzo's concept of das-in-der-Welt-sein (being in the world) expressed in The Book of Tea to describe Zhuangzi's philosophy, which Imamichi's teacher had offered to Heidegger in 1919, after having studied with him the year before.
There are also recent signs of the reception of phenomenology (and Heidegger's thought in particular) within scholarly circles focused on studying the impetus of metaphysics in the history of ideas in Islam and Early Islamic philosophy; perhaps under the indirect influence of the tradition of the French Orientalist and philosopher Henri Corbin.
In addition, the work of Jim Ruddy in the field of comparative philosophy, combined the concept of Transcendental Ego in Husserl's phenomenology with the concept of the primacy of self-consciousness in the work of Sankaracharya. In the course of this work, Ruddy uncovered a wholly new eidetic phenomenological science which he called "convergent phenomenology." This new phenomenology takes over where Husserl left off, and deals with the constitution of relation-like, rather than merely thing-like, or "intentional" objectivity.
Phenomenology has at least three main meanings in philosophical history: one in the writings of G.W.F. Hegel, another in the writings of Edmund Husserl in 1920, and a third, deriving from Husserl's work, in the writings of his former research assistant Martin Heidegger in 1927.
The difference in approach between Husserl and Heidegger influenced the development of existential phenomenology and existentialism in France, as is seen in the work of Jean-Paul Sartre and Simone de Beauvoir. Munich phenomenologists (Johannes Daubert, Adolf Reinach, Alexander Pfänder in Germany and Alfred Schütz in Austria), and Paul Ricoeur have all been influenced. Readings of Husserl and Heidegger have also been crucial elements of the philosophies of Jacques Derrida and Bernard Stiegler.
Although the term "phenomenology" was used occasionally in the history of philosophy before Husserl, modern use ties it more explicitly to his particular method. Following is a list of thinkers in rough chronological order who used the term "phenomenology" in a variety of ways, with brief comments on their contributions:
Later usage is mostly based on or (critically) related to Husserl's introduction and use of the term. This branch of philosophy differs from others in that it tends to be more "descriptive" than "prescriptive".