Modern art, or a so-called “modernist” one, started with the realist Cézanne, the symbolist Gauguin and the expressionist Van Gogh. To this day, as long as it is still art, it remained a continuation of these three main trends. The artistic modernism is considered to be a general phenomenon of “moving away from tradition”. However, the problem is a bit more complicated. Was the Renaissance a breaking with tradition? Stylistically there seem to be no doubt: there is no link between Bramante's tempietto and a Gothic-style cathedral. Did Leonardo break with Christianity though? Did Michelangelo?

The most prolific phenomenon of the 19th century was the paradox of positivism: the more significant effects produced the scientific research and the broader was human knowledge—the poorer was the idea we had of the Universe. The empiricist positivism was based on an axiom: nothing exists of which there is no sensory evidence and that cannot be scientifically proven. If the 19th century man had possessed any kind of divinely-revealed knowledge about the reality, then the positivism (surprisingly enough) would not have scientifically completed this knowledge but would have rather narrowed it. Unfortunately—however unpleasant it is—most people are not able to understand nor to verify the scientific knowledge (e.g. the theory of relativity formulated in 1905). It does not mean this knowledge is worthless; however, a universal notion of it is the same as of any other believed to have been divinely revealed.
The turning point brought by the 19th century deprived people of a transcendent base but it could not solve any of the everlasting conflicts. Artist is neither a scientist nor a philosopher. They do not approach problems scientifically, they do not carry out logical speculations; they give a testimony instead. With their very being and the very creation of impractical objects they ask questions regarding the true meaning of life.
The transcendence, worshiped as a part of organized religious movements, has been taken away by the 19th century. Social sciences were dominated by the pragmatism of Charles Sanders Peirce (1839-1914) and William James (1842-1910) which implied instrumentalism and benefits resulting from human actions as the criteria for truth. That instrumentalism would assess the legitimacy of metaphysical theories according to their practical consequences. In psychology, the behaviorism of Ivan Pavlov (1849-1936) and Edward Lee Thorndike (1874-1949) was particularly successful—it would build theories on human psyche upon truths derived from a research on animals' reflexes.
The progressivism of John Dewey (1859-1952) seemed to be the biggest achievement in the area of education. That is, a naturalist education limiting the role of upbringing and set on the unfettered development of personality. As for the philosophy, the intuitionism of Henri Bergson (1859-1941) was an attempt to tackle the positivist rationalism. It was also one of the so-called “philosophies of life”; it recognized a pantheistic élan vital to be the major driving force, however it questioned mind's claims towards comprehensive explanations of the mystery of life. Bergson thought that science, formulating unchangeable laws, creates a static image of reality—whilst its character is rather dynamic and human intuition is predisposed to recognize the laws ruling it.
Views of such thinkers like George Santayana (1863-1952), a representative of the critical Realism, meant a triumph of spiritualization of philosophy. Santayana claimed that the world actually exists, but is does not reveal itself entirely to the senses—it is too complex for them to be accessible (for example, he said, human hearing cannot perceive the ultra-high tones heard by dogs nor the ultra-low tones heard by elephants).
These post-positivist trends created the atmosphere which encouraged artists to present their own vision of reality. Some went for examining the structure of reality, subject to never-ending transformations, and for the very mechanics of discovering it. Material reality in motion and a possibility of its unbiased display were the themes for Cubism, and Futurism—loosely bound with the former. Others, sensing higher levels of existence above the biological one, tried to introduce them by creating a set of basic symbols of universal meaning. This concerns, e.g., suprematists and surrealists. Another group, the most numerous, reached a conclusion that world had lost both its rational and metaphysical bases; the man was standing out alone, facing the mystery of existence—which meant a ceaseless conflict (Fauvism), requiring to be expressed. The feature shared by almost every modernist trend was the search for spirituality in mysticism, occultism and exotic Eastern religions—which did not have any unfortunate associations with a rigorous Christian ethics, seen as “fetters”.
The entire Modernism, however, shared one feature with the great artistic tradition: it supported the cult of art as an exceptional phenomenon and, paradoxically enough, assigned an exceptional mission to the artist as well—making him a romantic prophet of the future time. This is probably the reason why almost all of the artists considered to be symbols of artistic revolution and total iconoclasts—such as Pablo Picasso, Kazimierz Malewicz, Piet Mondrian or Salvador Dalí—in the depths of their work were in fact classicists; looking for order, symmetry and harmony.

Dada was the only trend that distinguished itself by every single feature, from the rest of Modernism. It was a trend—and some will probably feel outraged now—lacking of any artistic importance (its essential symbol being an urinal promoted to the rank of a work of art). However, Dada became the only landmark of Modernism—seen rather as a kind of breaking than a continuation. Dada became the anti-art and anti-culture essence. It fundamentally changed the art of the 20th century and remained lively until present day: since it did not grow out of a discourse performance, but from playing tricks. Its artistic value is null; its attractiveness, however, could be compared to the one which would bring crowds to the Colosseum for gladiator fights. It was created by young, intelligent and witty people; tradesmen and critics were the ones who gave a boost to the phenomenon.
The most interesting problem of Modernism, and the most important from the point of view of art history, is its connection with politics. Anarchistic origins of Dada are not surprising (although the anarchism implied more genuine reflection). It is puzzling that two almost identical totalitarian systems originating from the socialism: Communism and Nazism, based their propaganda on classic models. The Stalinist and Nazi socialist realism is actually not considered to form part of Modernism, which is associated with deeper humanist motivations. It is being pointed out that Nazism regarded the entire modernist art as degenerated. However, it does not clarify the causes because of which the so effectively true modernists served communism.