This is not an invitation to prophecy but a demand for a universal outlook upon the world. (Space, Time and Architecture, 7)

In what was originally his introductory lecture, ‘The Role of History Today’, in his Charles Eliot Norton lectures at Harvard on “Art and Architecture”, 1938, and later became the first chapter of Space, Time and Architecture (STA), Sigfried Giedion sets out the case for a relativity theory of the domain of human experience — aka the domain of “the world of history”.

There are no “absolute points of reference”:

Absolute points of reference are no more open to the historian than they are to the physicist; both produce descriptions relative to a particular situation. Likewise there are no absolute standards in the arts: the nineteenth-century painters and architects who thought certain forms were valid for every age were mistaken. (5)

The historian cannot in actual fact detach himself from the life about him; he, too, stands in the stream. The ideal historian — out of the press of affairs, au-dessus de la melée, surveying all time and all existence from a lofty pedestal — is a fiction. The historian, like every other man, is the creature of his time and draws from it both his powers and his weaknesses. (6)

Unfortunately the historian has often used his office to proclaim the eternal right of a static past. Ever since man recognized the impossibility of making objective judgments, such an attitude has been discredited. (6-7)

History is not simply the repository of unchanging facts, but a process, a pattern of living and changing attitudes and interpretations. As such, it is deeply a part of our own natures. To turn backward to a past age is not just to inspect it, to find a pattern which will be the same for all comers. The backward look transforms its object; every spectator at every period — at every moment , indeed — inevitably transforms the past according to his own nature. (5)

History cannot be touched without changing it. The painters of our period  have formulated a different attitude: lo spettatore nel centra del quadro. The observer must be placed in the middle of the painting, not at some isolated observation point outside. Modern art, like modern science, recognizes the fact that observation and what is observed form one complex situation — to observe something is to act upon and alter it. (5-6)

But intelligibility is not the same thing as building upon “absolute points of reference”:

Historians quite generally distrust absorption into contemporary ways of thinking and feeling as a menace to their scientific detachment, dignity, and breadth of outlook. But one can be thoroughly the creature of one’s own period, embued with its methods, without sacrificing these qualities [of scientific detachment, dignity, and breadth of outlook]. Indeed, the historian in every field must be united with his own time by as widespread a system of roots as possible. The world of history, like the world of nature, explains itself only to those who ask the right questions, raise the right problems. The historian must be intimately a part of his own period to know what questions concerning the past are significant  to it. (6) 

So it is that “scientific detachment, dignity, and breadth of outlook” are possible, and are possible only, on the basis of the relativity of human experience:

We must take our departure from a large number of specialized disciplines and go on from there toward a coherent general outlook on our world. (17)¹

The key is to discover some co-variance which functions across all the varieties of “specialized (…) outlook” (thereby establishing a continuum in which also our own outlook is situated)²:

Today we consciously examine the past from the point of view of the present to place the present in a wider dimension of time, so that it can be enriched by those aspects of the past that are still vital. This is a matter concerning continuity… (7)

In 1908 the great mathematician Hermann Minkowski first conceived a world in four dimensions, with space and time coming together to form an indivisible continuum. His Space and Time of that year begins with the celebrated statement, “Henceforth, space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality”.  It was just at this time that in France and in Italy cubist and futurist painters developed the artistic equivalent of space-time in their search for means of expressing purely contemporaneous feelings. (14)

Each period lives in a realm of feeling as well as in a realm of thought, and changes in each realm affect the changes in the other. Each period finds outlets for its emotions [the realm of feeling] through different means of [artistic] expression. Emotions and expressive means vary concomitantly with the concepts [in the realm of thought] that dominate the epoch. Thus in the Renaissance, the dominant space conceptions [in the realm of thought] found their proper frame in [artistic] perspective [in the realm of feeling], while in our period the conception of space-time  [thought] leads the artist to adopt very different means [feeling]. (16) 

The degree to which its methods of thinking and of feeling coincide [aka, establish some kind of balance] determines the [particular sort of] equilibrium of an epoch. (17)

Present-day happenings are simply the most conspicuous sections of a continuum; they are like that small series of wave lengths between ultraviolet and infra-red which translate themselves into colors visible to the human eye. (7)

Such a general theory of experiential relativity enables us to overcome relativity in the vulgar sense:

A transition period may affect two observers in very different ways. One may see only the chaos of contradictory traits and mutually destructive principles; the other may see beneath all this confusion those elements which are working together to open the way for new solutions. It is not a simple thing to decide between two such judgments, to determine which has emphasized the essential marks of the time. We need some objective guide to what is going on in the depths of the period, some sign by which we can determine whether or not its dispersed energies are being brought into united action.  A comparison of the methods which govern its [correlated] major activities, its thinking and feeling, may afford us such an objective criterion.³(12)

But sensing such a possibility and communicating it are two different things: 

In both contemporary science and contemporary art it is possible to detect elements of the general pattern which our culture will embody. The situation is a curious one : our culture is like an orchestra where the instruments lie ready tuned but where every musician is cut off from his fellows by a soundproof wall. It is impossible to foretell the events that will have to come before these barriers are broken down. The only service the historian can perform is to point out this situation, to bring it into consciousness. (17)

Still, historians have a responsibility to such “interrelationship”, both in establishing focus for their subject matter and in their dedication to communication with their contemporaries:

The historian detached from the life of his own time writes irrelevant history, deals in frozen facts. But it is his unique and non transferable task to uncover for his own age its vital interrelationships with the past. (6)

A period may be dominated by transitory or by constituent [aka, interrelational or orchestral] facts; both alternatives are open. There is, however, no doubt which of these two classes of trends is the more likely to produce a solution of the real problems of the age. (19)