Number is the origin of all things. The enthusiasm for numbers is the origin of the occidental tradition of science. It became the Leitmotif in our attempts to understand nature theoretically, i.e. within the framework of natural science.

The history of psychology often refers to an event that is strongly related to this enthusiasm for numbers: Gustav Theodor Fechner’s sudden insight on the 22^nd of October 1850. According to Fechner, he was still in bed when he had a sudden insight of a world in which body and soul, mind and matter, find their mystic unity within number. In this vision, „the schema of geometrical series was an expression of the real interrelation of soul and body“.

Pythagoras must have had a similar experience when he passed by a blacksmith's shop and recognized the musical intervals in the sound of the hammers: the octave, the fifth, and the fourth. Weighing the hammers, he found that their weights stood in a relation of 12:9:8:6. At home, he re-examined this observation using strings, which he stretched with weights of the same proportions. These strings, as well as investigations of other instruments, confirmed his observation. It is a nice story, handed down to us by Iamblichos. It demonstrates that it is possible to find the unity behind diversity, to find simple and invariant regularities behind the manifold of appearances, which can only be expressed in numbers, and that the subjective qualities of tones too have their origin in the relations between numbers. In the presence of these facts, we may generously overlook that physical realities alone call into question the authenticity of this anecdote.

In physics, the Leitmotif of strongly connecting the development of theories to the ‘Quantitative’ originated in Pythagoras and subsequently evolved over a long period. However, in psychology this Leitmotif was adopted rather quickly. In 1860, an unambiguous statement was made in Leipzig:

“As a matter of course, we cannot in general deny that the mind is subject to quantitative principles. This is because apart from distinguishing stronger and weaker sensations, we can also distinguish stronger and weaker intensities of drive, higher and lower degrees of attention or vividness of recollections and fantasies, as well as different stages of consciousness and different intensities of individual thoughts. … Consequently, the higher mental processes can - in much the same way as sensory processes - be measured quantitatively, and the activity of the mind can be measured quantitatively in its entirety as well as in its components.”

The man who formulated this statement was an experimental physicist, who had already gained a reputation for his achievements in electrophysics. He was a private scholar of philosophy with his head in the clouds and almost the caricature of a savant in his personal habits. He was a wandering spirit - incessantly writing, pondering and writing, as a slave to the themes that had captured his attention and that dominated and compelled him to the point of total exhaustion. His biographer and nephew Emil Kunze describes him as “genuine and earnest”, as a deeply sensitive natural mystic attempting to find the wholeness in all things. As he wrote in a letter in 1825, he wanted to see the wholeness whilst looking at the details. Fechner felt a deep distrust for Bacon’s dissecare naturam, and was against the dissection and decomposition of nature, where the components of natural phenomena were isolated to fit into a theoretical system in order to comprehend the original order behind the diversity of phenomena. With his metaphor about light, Fechner describes his idea of distinguishing Day Vision from Night Vision. He stresses the importance of “Day Vision”, in which “sensual phenomena form a unity of immediate experience”. He would not accept the platonic concept of reason being superior to the senses. Night Vision was equivalent to an estrangement from sensual experience. He did not search for some abstract truth behind sensual phenomena, but he wanted to comprehend the phenomenal order that is inherent to our conscious self, and he tried to achieve it by applying inductive methods and drawing conclusions from analogies. For him, Night Vision was equivalent to the partition of a unity and the estrangement of abstraction, and he compares it to the “search of the mirror-image behind the mirror”.

Fechner’s zeal was to reconcile opposites and to reunite estranged parts, as for example natural science and religion, Day and Night Vision, the inner and outer side of nature, and the objective and the subjective perspective. Quite like Goethe, he opposed a characteristic feature of natural science, namely the disintegration of nature, its idealisation and utmost abstraction that serve to estrange it from its original phenomenology.

Can we – taking Fechner’s real concern seriously – place Fechner’s psychophysics in the tradition of Mathesis universalis at all? Would this not amount to ignoring his dearest ambition, trying to fit him into Procruste’s bed of tradition, which actually constitutes the opposite of Fechner’s fundamental metaphysical position? – Yes, it would, and what’s more: Any categorization along the lines of previous traditions would wrong Fechner because it is, frankly speaking, utterly impossible to respect all of Fechner’s facets. Whatever we do to squeeze the whole Fechner into the bed of any tradition – at least half of him would always end up sticking out of the other end.

Fechner contemplated many traditional philosophies at the same time. However, even with various references to previous traditions, his reception of philosophy and general academic conception was not very pronounced. In a rather eclectic way, he selected from various sources whatever he deemed suitable for constructing his personal vision of wholeness. He knew about his eclectic and syncretistic approach to philosophy and therefore rejected the title of a philosopher for himself.

Among the wide range of ideas that Fechner contemplated, one philosophy stood out: the idea of the Allbeseeltheit (the animation) of the universe - reaching from Thales, Plato, Aristotle, and the Stoics to Leibniz. Fechner rejected mechanistic-materialistic concepts, especially the reductionistic program of establishing physiology on a physico-chemical footing, as proclaimed by Carl Ludwig, Hermann von Helmholtz, Ernst von Brücke and Emile du Bois-Reymond in 1847. In the same year, Carl Vogt presented a thesis that indeed must have sounded quite frivolous to Fechner - “that all those capabilities we subsume under the name of soul-related activities are merely functions of the brain. Or, to speak boldly, the relation between thoughts and brain is of the same nature as the relation between bile and liver, or between urine and kidneys”. Nevertheless, his idealistic position was inconsistent enough to allow him to accept that the body is the bearer, the foundation and the organ of the soul. Like Leibniz, Spinoza and many others before, Fechner was convinced that reality based on a monistic concept; like Leibniz, he saw a continuum between perception and apperception. Although he shared Leibniz’ view that the death of a human being was a transition from an appercepting to a sleeping monad, where man descends down to the lowest stage of the hierarchy of monads, he however rejected Leibniz’ philosophy in general. This syncretistic approach is typical of Fechner – it was only towards Spinoza that he felt a strong affinity. If one tried to follow Fechner’s references in the intellectual history, one would have to traverse philosophia naturalis, the philosophy of religion, mysticism, and romantic theory of nature, in all directions.

I will now briefly outline Fechner’s contact with natural philosophy, because this will provide us with some insight on his approach to the development of his Maßformel. In February 1820, Fechner became acquainted with Lorenz Oken’s romantic philosophy of nature, a biologist among the natural philosophers, whose personality as well as his works held a great fascination for the public at the time. According to Fechner’s diary, the natural philosophy of Oken “filled me with such enthusiasm that it influenced my thinking for a long time. … In my view a new light had dawned upon the entire world and the sciences of the world, and I felt like dazzled from this light.”

In Oken’s work, we find many things that influenced Fechner in the development of his number mysticism. For Oken, mathematics was the mother of sciences; its fundamental principle is the “Zero = 0”. The universality of all sizes, numbers and figures is potentially present in the Zero. The potential that is intensive and ideal in Zero becomes extensive and real in the actual number. In becoming real, the Zero will be divided into plus and minus, into “postulation” and “negation”, into positive and negative. By way of postulation and negation – setting the numerical series 1 + 2 + 3 … + n accordingly – God transforms into plus and minus, while he remains the ‘no-thing-ness’, and therefore himself.

To our ears, such attempts to rationalize mystic experience seem to resemble merely an aberration of language. Within the darkness of number mysticism we can, however, find thought figures that can be expressed in numerical series, and that inspired Fechner to develop his Maßformel.

“I was dazzled from the light,” he writes, “for sure I did not comprehend all of it, but suddenly I had the notion of a great united Weltanschauung (world view).” Thus, his attitude changed towards a uniform philosophy, and he abandoned the concept of romantic natural philosophy. In his diary we read, “Natural science was not on my way … gradually, the direction I took became clearer, since it occurred to me that this might be the only way to obtain transparent, correct and fruitful results in natural sciences. … Nevertheless, I still believe in the one-ness of nature and its spiritual animation.”

There are references to Oken’s number mysticism in Fechner’s major philosophical work Zend-Avesta. Oder über die Dinge des Himmels und des Jenseits (Zend-Avesta. Or on the Things of Heaven and the Hereafter, published in 1851. The short supplement Kurze Darlegung eines neuen Prinzips der mathematischen Psychologie (A Short Introduction to a New Principle of Mathematical Psychology) already contains Fechner’s idea about the Maßformel, and thus the core element of his psychophysics. Following his typical way of analogizing, he compares the body with a numerical series of higher order and the soul with a numerical series of lower order. Henceforth, the activities of the soul are less complex than the corresponding material processes. In mathematical terms, the “soul is acting inside the body” according to the simplest laws of numerical series, whereas the series of higher order represent the more complex physical organisation. All series, however, are “made of the same material”.

The number series quite fascinated Fechner, because to him they seemed to reflect the relation between the element and the whole, between the superior and the inferior, and the dynamic change between higher and lower levels of complexity in the organisation of the world. In the course of this, it was almost inevitable that Fechner discovered algorithms, which he regarded to be a suitable base for his number mysticism. Now, he could support his idea that all that exists can be conceived in terms of numerical series. The logarithmic tables became Fechner’s daily lecture and, according to Stanley Hall, almost his evangelism. These tables suited him perfectly, since he was, according to his own description, “a very untalented arithmetician himself”.

This was the ground from which Fechner’s psychophysics was to emerge. From there, however, we have some more work to do until we can finally incorporate psychophysics into the tradition of Mathesis universalis. On our way, we must neglect Fechner’s comprehensive approach and instead excerpt a single element, which we will investigate separately.

Fechner’s way of mingling natural-scientific methodology with animistic and teleological concepts, with number mysticism and mystic cosmology, hardly differed from that of other great scientists. Newton, for instance, was an enthusiastic and devoted alchemist who, at nighttime, conducted experiments in order to transmute metals and enciphered the results in a secret code afterwards. Another example is Kepler, who writes in his Harmonice Mundi about number mysticism and investigations into the harmony of celestial bodies and the music of the planets. Apparently, the metaphysical sobriety of a scientist like Galileo ought to be regarded as rather exceptional in the history of natural sciences.

In its imponderable differentiation and development, natural sciences are oblivious to the intentions and passions of those who contribute mostly to their advancement. The alchemy of Newton did not persist and neither did the spherical harmony of Kepler. The course of history follows its own logos, advancing the ideas that are to last – i. e. ideas that enhance the explanatory vigour, depth and width of theories – and eliminating those that are idiosyncratic. Likewise, Fechner’s metaphysical worldview was a very peculiar mixture of rather disparate traditions; it was idiosyncratic and exceptional, and therefore inappropriate for the establishment of schools or subsequent developments.

In the history of psychology, however, the dynamic mixture that Fechner produced by combining the mysticism of his worldview with the sober and straightforward methodology in the natural sciences, remains unrivalled. Here, we have two incompatible methods of gaining an understanding of ourselves. Ever since man has transformed himself into the subject of his theoretical curiosity, he has been pondering over possible ways to uncover the truth about himself. He developed many ways to examine the very nature of the human mind. Two ways, however, stand out in the radicalism and totality of their scope: firstly, mysticism, which intends to reveal the depth of the soul by means of contemplative introspection. Secondly, natural science, which regards the human psyche as a natural thing and attempts to measure the psyche objectively from without.

Fechner was determined to follow both ways at the same time; he wanted to combine and reconcile instead of deciding in favour of one of them, because, according to the appropriate characterization of Gerd Mattenklott “the spiritual presupposition for achieving his individual productivity would have to be a permanent crisis”. It must have been tragic for him to see that history acknowledged only those aspects of his philosophy that he himself regarded as mere vehicles to convey his views, and which were not the core of his philosophy. His actual core believes, on the other hand, came to be rather ignored in the course of further developments, much like the alchemy of Newton.

Fechner and his radical combination of mystical natural philosophical views with various empirically orientated scientific research methodologies present a discontinuity in the history of psychology. However, this discontinuity is often misrepresented in the conventional history of psychology, because the seeds for the establishment of a natural scientific psychology had been sown a long time before Fechner, especially during the dispute about the concept of perception.

A thousand years ago, the Arab natural philosopher and mathematician Alhazen developed the idea of the unconscious inference. Today, we can find this central concept of perceptual psychology in the theorem of Bayes. Alhazen found out that the process of visual perception could not be straightforwardly reduced to the interplay of geometrical processes, but that non-geometrical psychological processes must participate. The natural philosophers of the 17^th century were familiar with the work of Alhazen, which included a detailed description of psychological mechanisms as mediators between geometry and experience. Alhazen supposed that, due to evolutionary development, judgement processes were occurring so rapidly that we were no longer able to recognize them. Philipp Melanchthon, who was probably the first to have used the term psychology 500 years ago, regarded psychology as being part of pneumatology, the theory of spiritual beings, and therefore as being part of the philosophia naturalis, which is the science of all natural things.

Likewise, most authors of the 18th century regarded psychology to be a natural science. Hume, for instance, had an entirely naturalistic approach to psychology, regarding his methods and his concept of explanation as equivalent to those of Newton. He even imagined himself to be the “Newton of psychology”. In the 18th century, quantitative studies were common practice – especially in the field of perception. Carus listed in his History of Psychology, published in 1808, more than 120 authors of the 18^th century, who had conducted quantitative psychological studies in order to systematize observations theoretically. Additionally, many systematic experiments on psychological issues had been carried out: In the year 1756, Johann Gottlob Krüger, for instance, outlined in his work Versuch einer Experimental-Seelenlehre (Essay on an Experimental Theory about the Soul) an experimental investigation of psychology, whilst neglecting any metaphysical aspects. There, he deals with the illusion that the moon appears much larger on the horizon than in the zenith of its orbit. Krüger found out that the perceived distance had an influence on the perceived size, while the size of the retinal image stayed the same.

To put it briefly, in the course of the gradual differentiation of natural-scientific psychology, Fechner did not represent a discontinuity at all. It was another aspect that accounted for his unique position in the history of psychology; in a more radical fashion than anyone previously, Fechner oriented towards the question of whether mental events could be quantitatively determined.

By this time the idea that a comprehensive method of quantification was an appropriate model for the development of theories had already fascinated natural scientists, especially physicists. Due to the great achievements of physics, each of the other natural sciences defined its validity according to its potential to express its concepts in quantitative terms. Now psychology was in a position to boast of interesting regularities and laws. It was, however, denied the status of a natural science due to a fundamental a-priori prejudice - the psychic was not regarded to be amenable to investigation by quantitative methods.

Before examining Fechner’s solution to this problem, let us briefly return to Pythagoras in order to investigate the quantitative in its relation to the qualitative in the history of natural science. We will throw a glance at Mathesis universalis, which will finally lead us to Fechner’s Maßformel.

Already Pythagoras had been fascinated by the similarity between numbers and certain relations in the real world, especially in acoustics and astronomical mechanics. Greek philosophers discovered that through the abstraction of numbers we could arrive at conclusions about the real world, and this with a precision that real conditions could never have provided. The most important step, however, was the transition away from merely operative counting and calculating towards the question “What is number?” This transition led the Greek philosophers to the development of a theoretical concept of number and to the conclusion that their conception of number is subordinate to the concept of magnitude. Those two concepts – number and magnitude – represented the fundamental roots of natural-scientific and mathematical thinking. From this basis, both mathematics and physics evolved, and the natural sciences could find a strong foothold in mathematics and it was due to this firm basis that physics achieved its theoretical success.

In physics, the classic separation between quality and quantity had dwindled early because these terms were subject to a continuous redefinition. Differences in quality were attributed to differences in quantity, i.e. differences in geometrical structure or in number.

The Pythagorean idea to seek the wholeness of the world in an abstract harmony had generated a new ideal of cognition. This ideal lasted throughout Western history of ideas. It recurred in the work of Cusanus, who emphasized that amongst all the symbols, of which the human mind is capable of conceiving; only mathematical symbols will persist. Cusanus found an etymological relation between the term ‘mens’ (mind) and the term ‘mensura’ (measurement), therewith anticipating a belief that Kepler later concretized: in the same way as the eye perceives colours and the ear perceives tones, human mind strives towards the perception of the quantitative.

This Leitmotif, persevering throughout the entire history of Western philosophy, postulated that only through quantitative analysis was the human mind able to conceive of the order behind the variety of phenomena, and that this variety can be consolidated into a unified whole. This idea finds its symbolic culmination in the 23-year-old Descartes who, in his famous dream on November 10^th in 1619, had the vision or desideratum to unite all of natural science under the roof of mathematics, formally uniting all principles of nature in a Mathesis universalis. In his work Regulae Descartes describes this enterprise: “I came to see that the search for order and measure belongs to this Mathesis, whereby it is absolutely irrelevant whether this measure is expressed in numbers, figures, astrological constellations, tones, or any other objects whatsoever.”

This Leitgedanke of a universal theory of measures and relations, in which the natural sciences show an increasing trend towards differentiation and dissociation from immediate experience and ought to form a methodological unity, has since been a characteristic of the development of modern natural sciences. The Mathesis universalis – which Max Bense appropriately characterized as “generalized mathematics of non-mathematical objects” – became a Leitfigur that shaped the entire tradition of modern natural science and its relation to mathematics from Pythagoras, Kepler, Descartes, Leibniz and Newton.

Now, which place can we assign psychology within this tradition? Is it not all too obvious that the architectus divinus has precisely not subjected the human mind to the regularities and laws of other natural sciences, which in fact render possible their mathematical treatment in the first place? Is it not – lets once more word the traditional philosophical prejudice – exactly the dichotomy between quality and quantity that is the landmark of the difference between the physical and the psychological? Or did Salomon, the God of Wisdom, also organize the psycho-physical in numero et mensura et pondere, according to number, measure and weight?

This is where Fechner’s significance in the history of psychology is most striking. He was the first to radically formulate the question of the measurability of sensations, simultaneously developing operative methods to verify it empirically. In contrast to all those before him who held that the nature of all knowledge is mathematical and that things are based on numerical relationships, he insisted on proving the correctness of this approach by empirical studies. Like Kepler, Fechner was a mystic, prepared to subject his metaphysical speculations to empirical evaluations, or to discard them if they failed to stand the test in the field of observations and facts.

In order to achieve his goal of finding “a measurement for sensation”, however, Fechner needed a unit of measurement that enabled him to express the magnitude of a sensation in terms of a “multiple of the same thing”. He based his search on the assumption, that we are able to make judgements about the “equality in the field of sensory perception”. According to him, this measure must not necessarily be a psychological measure, because “it will never be possible to find two sensations that are exactly congruent, so as to deduce one sensation from the other. A measure for sensations can, nevertheless, be found if we determine a comparison value that reflects sensations in the same way as the length of a yard reflects the matter of a yard.” Fechner found this comparator in the equation he named “Weber’s Law”. Even if in the field of psychology the mathematical operation of adding values was impossible, Fechner proposed another solution to find a unit of measurement: to count the gradations of the smallest discriminable difference, the so-called just noticeable differences above a threshold of discriminability. Based on this definition of a unit of measurement, Fechner derived from Weber’s law his “Massgesetz der Empfindung” and his “Unterschiedsmaßformel”, according to which the magnitude of sensation was proportional to the logarithm of the magnitude of the stimulus related to its threshold value.

The assumptions Fechner based his Maßformel upon remained controversial, the great scientists of his time like Gauß, Helmholtz, Mach, Brentano and Hering distrusted either specifics or even the whole of his line of argumentation. Von Kries reproached Fechner with simply combining a physical experiment with arbitrary convention. Despite all of these reservations, however, the essential impulse for the development of a quantitative and experimental psychology had been given.

Fechner’s methodological approach involved the application of judgement variations in order to deduce metrical information about internal subjective magnitudes. Together with his method of average error – he was the first to introduce the concept of the average distribution of errors to psychology – these were the first essential steps for the development of methods on the advancing field of experimental quantitative psychology. Fields as special as learning theory, decision theory, sample theory, and adjustment measurement cannot be imagined without the concepts based upon this formal development of tradition.

In psychophysics, the reception of Fechner’s ideas met with far less approval due to the metamorphic influence imposed by the behaviouristic and elementistic philosophies of Stevens. Inundating the market with publications, Stevens attempted to polemically distort historical facts in order to adapt the historiography of psychology to his own purposes. Like before in the case of investigations about the so-called ‘levels of scales’, he tried to subject psychophysics to a research paradigm that gave rise to maybe one of the most unfruitful phases in the history of perception psychology.

In contrast to Fechner’s metaphysically motivated zeal, Stevens’ interest in the construction of scales was related to an elementary misconception of the role that ‘sensory measuring instruments’ played in perception. He claimed that some kind of sensory measuring instruments performed an initial step during the process of perception by ‘informing’ the sensory system about elementary physical stimulation. This theory would merely reduce psychophysics to some kind of perceptual physics, thereby completely neglecting the complex functional aspects that characterise the adaptation of organisms to their environmental conditions.

Gestalt psychologists had already proven the inappropriateness of this conception in many cases. Only during the 1980’s and in the course of the Marr revolution, that Stevens’ paradigm, which focussed on scales and resulted in a somewhat sterilization of the field of perception research, could finally be abandoned.

With the preparatory work carried out by Gibson, Brunswik, Kardos and Bühler it was now possible to merge a functionalistic perception theory with concepts of computational analysis. Thus, scientists returned to the concept of perception as Fechner, Helmholtz and the Gestalt psychologists had interpreted it since the 17^th century, and developed it further.

The effects Fechner’s ideas had on psychology are as complex and diverse as their evolution. Fechner’s radical investigations into the measurability of mental magnitudes and the solutions he proposed, however, matured to become a completely independent field of subject matter. In an unexpected synthesis with Helmholtz’ abstract inquiry into the term ‘measurement’ and following the tradition of Mathesis universalis, Fechner’s psychophysics dealt with the abstract numerical representation of empirical magnitudes: the theory of abstract measurement. Of course, Fechner did neither intend nor foresee such a development.

Helmholtz was convinced that “the only thing which outer and inner world had in common was their mathematical base”. He claimed that, within the natural sciences, mental processes were subject to theoretical investigation only in as far as they could be expressed in mathematical terms. In the year 1887, he published his work Zählen und Messen erkenntnistheoretisch betrachtet (Epistemological Reflections on Counting and Measuring), which regarded only physical issues, leaving aside the problem of the measurability of mental magnitudes. In this work he tried to develop abstract methods for measuring magnitudes as such, in order to determine epistemological and formal standards that were applicable for any kind of measurement of magnitudes. Considering the very different nature of the contributions Fechner and Helmholtz made, it seems surprising that their advancement and synthesis has lent such a new strength to Mathesis universalis, now involving psychological magnitudes as well.

The synthesis of Fechner’s ideas with those of Helmholtz initially revealed a great need for conceptual clarification: Fechner aimed at the quantification of psychological magnitudes through the analysis of fluctuations of judgements, whereas Helmholtz tried to define the traditional concept of the extensive magnitude. In the process, it became more and more clear that the notion, which in numerical terms was defined the ‘quantitative’, was only the mirrored reflection of qualitative relations between objects. The important consequence of this was the complete redefinition of the traditional dichotomy between quality and quantity. This analysis resulting in the redefinition of the concepts quality and quantity completely abolished the a-priori prejudice that the quantitative determination of psychological magnitudes was impossible because the mathematical addition of these magnitudes was impossible, too.

These concepts yet required more clarification in order to arrive at the so-called ‘Scott-Suppes paradigm’, the standard theory of fundamental measurement. Further steps were still required to develop the probabilistic theory of measurement, and to generalize the concept of extensive measurement into the additive conjoint measurement.

Fechner and Helmholtz were the forefathers of Mathesis universalis, i.e. a “generalized mathematics of non-mathematical objects”, which also included psychological magnitudes, too. Because the two initially incompatible concepts related to very different perspectives, their clarification was the only way to integrate them into an independent theory of magnitude measurement. From this evolved an abstract measurement theory, the differentiation of which is nowadays so distinct that it can hardly be regarded as belonging to psychology as such. It is now an independent research area, which in the tradition of Mathesis universalis includes all the sciences that, according to Descartes, “examine measurement and order”, regardless of whether we examine psychological, physical or economical magnitudes.

I have attempted to assign Fechner an appropriate place between Pythagoras and the present – in spite of the fact that the scientist Fechner is unique and cannot to be placed anywhere due to his crossing the borders between irreconcilable traditions. I have managed to classify at least a large proportion of Fechner. This symposium will aim at investigating the whole Fechner. In order to assign him some place in the tradition of Mathesis universalis, I have had to extract an aspect that he only used as a vehicle to convey his philosophy, but which did not embody his philosophy as such. I had to extract that aspect from his syncretistic worldview, which he did not expressively formulate but experienced rather intuitively, describing it in analogies.

At the end of his long commitment for a unified worldview, Fechner had to realize that his philosophy would not lead to subsequent development. Nevertheless, his philosophy gave a productive impulse to the future development of his subject field. It had been Fechner’s most fruitful and greatest contribution to the history of natural sciences. He was the first to formulate the problem of the measurability of psychological events in a radical manner, and he proposed a solution to it.

In the great tradition of Mathesis universalis and right from the beginning as the central Leitmotif in the evolution of the natural sciences, Fechner’s achievements are extraordinary, though he himself would probably accuse us of misrepresenting his dearest ambition. We can even go as far as saying that the failure of his zeal gave the most fruitful impulse to his field of subject, helping us to understand the importance of extending natural scientific methods onto mental processes.

While attempting to integrate the perspective of the subjective self into natural science, Fechner foresaw many findings in phenomenology. He was doomed to failure, however, because the basic concept of natural sciences during the creation of theories is objectivity. The theoretical image relies on an independent perspective, i.e. the perspective of a third person. Therefore, the method of understanding mental processes in natural science is very specific. It is incomparable to other methods of understanding, because there is no tertium comparationis, with which a comparison would make sense in the first place.

To speak in terms of Fechner’s metaphor about light: we do not stand at the cross-roads between Day Vision and Night Vision. The Day Vision supports the unity of the consciousness of the self, and the Night Vision, applying abstract methods to disintegrate and divide this unity, intends to find the real order behind the phenomena. In the same way as day and night represent the laws of nature Day Vision and Night Vision represent the laws of the human mind. They show that human mind is capable of various ways of comprehension. Fechner’s heroic attempt at combining both ways of comprehending - the natural scientific method and the method of a unified conscious self - into one theoretical concept was doomed to failure. At the same time, it revealed that Day Vision and Night Vision could lead to a mutual advancement without, however, having to decide in favour of either of them. As Lichtenberg puts it ironically, the ways to reveal the mental are as wide as they are long.

This speech was presented by Prof. Mausfeld orally and in the German language to the ISP on the 19^th October 2001 and on the occasion of the Fechner Day marking the 200^th anniversary of G.-T. Fechner's birth. We are indebted to Karin Drews for her translation from the original German text and to Dr. Anneros Meischner-Metge of the Fechner Gesellschaft for her kind permission to use the text here.