In the phenomenological analysis, which departs from the perceptive act in order to get to consciousness, Husserl is driven to the analysis of the lived body, given that things display a variable orientation in relation to the absolute here instituted by one’s own lived body. It is noticeable that the latter has a unique preeminence in relation to other bodies or things, because it is the condition of possibility of the multiplicity of presentations of the other spatial objects, and because, in addition, it is not possible to move away from it. In contrast to the mere material body, Husserl characterizes the lived body as an animated body that is both the “carrier” of an ego and a physical body. It is thus doubly defined as a “psycho-physical unity”. Therefore, he distinguishes two attitudes from which it can be considered: an internal one, in which the animated aspect is predominant, and an external attitude, in which it is constituted as a physical body, comprehended as nature.

The lived body shows constituting functions that allow the very access to the world, to objects, and other subjects. The body that functions as an “organ of perception” [1] (p. 144) knows itself in its kinaesthetic freedom: it has the possibility of voluntary movement. This means that I not only experience a sensation of movement when I observe an insect, but that I can also be aware of this movement as “I move the eyes”. Kinaestheses are sensations of movement relative to one’s own body (i.e., and the impressions that take place when parts of the body or the organs of perception move). Every perception is consequently possible only through a “start of the ego” [ichliches In-Gang-Bringen] that consists of a “happening in the character of the ‘I can’ or ‘I do’” [GeschehenimCharakter des ‘ichkann’ oder ‘ichtue’] [2] (pp. 108, 164). Kinaesthesis refers to an autonomous type of happening that is possible or departing from the ego. Sensations of movement not only have a constitutive role for the appearance of the thing, but also participate in the appearance of the body itself, whereas at the same time, they are experienced as “located” in the body. Husserl took the descriptive content of this physiological concept because it is relevant for the phenomenological analysis of constitution, as it is clear that bodily sensations constitute an essential component of the experiential constitution of spatial corporality. In other words, sensations of movement accompany both the movement of the subject that perceives and the movement of the perceived object. Although unlike physical data belonging to other fields of sensation that enter into the unity of the appearance of the thing, kinaesthetic data do not belong to the “projection” of the thing. Therefore, as had already been mentioned, they constitute an autonomous type of subjective happening through which we are aware not only of the sensation but of a spontaneity of the ego as a principle of action.

The descriptive features of the lived body [Leib] and its distinction from the mere body [Körper], which equates in its conscious constitution to the experience of other physical bodies or things, reveal the essential place that kinaestheses have as “mediators” and defining components of the lived body: these kinaestheses permit precisely both the constitution of bodies or things and one’s own lived body, distinguishing it from the rest of the bodies as merely physical. In this sense, another differentiation emerges: that between causality and motivation. For Husserl, the notion of nature alludes to a specific spatial–temporal stratum of all experience that, therefore, founds all the superior strata of knowing and valuing. We recognize a stone or a tree as such because nature does not consist of a field of facts or appearances that we refer to as an in-itself without sense, but it is an intentional correlate, and we take it in its immediately constituted sense. The causality of nature then appears as “an empiric fixed regulation of coexistence and succession, always given in objective experience in the form of certainties of expectancy, as an expectant ‘that must come’ or ‘that must be together now’, i.e., after now such and such are already there from experience or have been before” [3] (p. 134). The fixed style of modifications that regulates the causality of nature is the prescientific foundation of all the inductions of the natural sciences that make both the laws of nature “valid in themselves” and their comprehension in mathematical concepts possible: it is the causality of bodies or things.

However, nature presents “a curious structure”: [4] (p. 439) among things there are also bodies that include a psychical component, above all, as animating components or as a life of sensations that “makes the body a carrier of tactile fields, of visual fields, of listening fields, etc., i.e., as a carrier of co-belonging groups of data of sensation that are immediately or mediately located on or in the physical body” [4] (p. 440), as has already been stated. Apart from this inductive-causal unity of objective nature that also includes in itself bodies purely considered as things, the experience through which we perceive a body as that of another living being, the principle of acts, gives those acts as acts of another living being, and, in that sense, psychical life is experienced as causally united with the body. Let us consider that some changes in corporality, as those in the sense organs when they are activated by pressure, touch, or eye movements, etc., involve some changes in psychic life, for example, in the life of sensations; and, conversely, we may consider that psychic changes involve physical changes (i.e., sleep-wakefulness). The body-soul unity also occurs as a natural-inductive unity [5] (p. 300); that is why the idea of a scientific psychology is justified, of a psychophysics that studies the laws of this unity [4] (p. 91), [5] (p. 105).

The fact that the unity of objective nature and the unity of body and soul are inductive-natural unities does not allow, however, to deduce that the unity of the soul is also inductive-natural. It would be an unjustifiable transposition leading to psychological naturalism (as it already occurred in the nineteenth century). For Husserl, the motivational connection is the fundamental law through which the unity of all the psychic—that assumes and includes one’s own lived body—is comprehended, and not only the unity of the personal spirituality. Therefore, passive strata of the soul such as association, and the totality of the life of feelings and impulses must be explained motivationally [1] (p. 220ff), [5] (p. 107ff). This leads to the distinction between rational and irrational or active and passive motivation [5] (p. 110, 331ff). This Husserlian consideration of psychic passivity as belonging to the realm of motivation is decisive. It is precisely the existence of a passive dimension in the psychic stratum that tends to be taken as a reason to adduce that the psychic stratum belongs to the realm of natural causality, as if the passivity or independence of will that is proper to natural facts were identical to psychic passivity. The passivity of association lacking ego activity and the passivity of the physical course of nature are placed at the same level, when, actually, association is a kind of motivation, the passive type. Husserl had noticed that the active spirituality, the activity of the ego with its freedom, even in appearance could not be identified with natural passivity and was reinterpreted by naturalistic trends as an apparent image of passive sources [5] (p. 333ff). The comprehension of this point is crucial if someone is to correctly appraise the contribution of the neurosciences. Within the framework of motivation there is, for phenomenology, on the contrary, an originarily continuity between psychic passivity and activity, as can be seen in the case of kinaesthesis: to be affected presumes an act and the consciousness of the “I can”. In this sense, because motivation regards the statute of all experience and consequently also that of the perception of external things, the causal connections are carried by motivational connections, which does not mean, however, that causality is to some extent an apparent structure that must be explained as motivation as suggested by Hume. On the contrary, it is transcendentally constituted as such in the subjective connections of the motivation of consciousness. Naturalistic perspectives failed because of their inability to take intentional events in their proper evidence and sense.

Consequently, has a human fact been accomplishedly comprehended when it has been scientifically explained? The experience of pain is one of the enigmatic touchstones for scientific analysis. Pain is the most personal and, depending on the case, bodily, of our experiences. There is no pain, as such, that is not experienced, or that is not felt. However, it is complex and difficult to show in what sense pain can be understood as a phenomenon. It is identified as experience [Erlebnis], as conscious experience, but it is also something that appears as object. The difficulty lies in answering to what extent pain can be considered an objective phenomenon. In phenomenology, the term “phenomenon” may have several different meanings:

There is no experience without a manner of appearance, without phenomenal multiplicities (i.e., there is no experience of an object without perspective). In turn, the appearing object is the phenomenon proper. That is, it is what shows itself to consciousness and as it is shown. The four senses in which “phenomenon” may be understood reflect the complexity with which things turn up. What appears is an object, but the act in which it appears does not depend on the object but on the subject (which is implicated in the other senses in which the phenomenon is understood). The experience [Erlebnis] is not anything that may be objectified inside the object, which means that the power of manifestation does not lie in the object itself. On the contrary, the originary perception of the body, except in specific situations (i.e., looking at oneself in a mirror), does not change perspective (not even in that example, because it is not the Leib but an external perception of the body, as Körper); I always have the same perspectives of my body: I cannot take a step back from it. This is the only object that resists being considered from new perspectives. In spite of that, this body is the correlate of all perspectives; it is the organ of perception, as has been said. It is the zero point of spatial orientation; from its dynamics there emerge the perspectives, it is the “here” from which all “theres” take shape. The body is the absolute dynamic “here”. For this reason, all senses of the phenomenon apply to the body: it is the only phenomenon that is called phenomenon in all senses because it is or it includes all that it intuits, the intuited, the elements of the intuition and the manner of the intuition.