The very beginnings of human thought, mind in its immediate and primitive stage, is sense perception: primitive man, through his senses, begins by registering and memorising the data immediately provided by his environment, without understanding the true nature, causal relationships, and laws which underlie them. From observation and experience, gradually the human mind proceeds to make a number of generalisations of a more or less abstract character. This process involves a long and laborious journey lasting several millions of years, extremely slow at first, but rapidly gathering momentum in the last ten thousand years. Yet despite the colossal strives made by thought and science, ordinary thinking remains on quite a primitive level.
When we first consider any subject, we first form a notion of the whole, without grasping all the concrete content and detailed interconnections. It is merely a general outline and a bare abstraction. Thus, the Ionic philosophers and even Buddhism intuitively grasped the universe as a constantly changing dialectical whole. But this initial notion lacks all definition and concreteness. It is necessary to go further and provide the general picture with a definite expression, analysing and specifying the precise relations of its content. It has to be analysed and quantified. Without this, science in general is impossible. This is the difference between crude, immediate, undeveloped thought and science as such.
At the dawn of human consciousness, men and women did not clearly distinguish themselves from nature, just as a new-born baby does not distinguish itself from its mother. Gradually, over a long period, humans learned to distinguish, to cognize the world, by detecting focal points in the bewildering web of natural phenomena surrounding them, to observe, compare, generalise, and draw conclusions. In this way, over countless millennia, a series of important generalisations were built up from experience, which gradually came to crystallise into the familiar forms of thought which, because we are so familiar with them, we take for granted.
Common, everyday thought relies heavily on sense perception, immediate experience, appearances, and that peculiar hybrid of experience and superficial thinking called "common sense." These things are normally sufficient to carry us through life. But they are insufficient to arrive at a scientific understanding, and, at a certain point, break down and become useless even for practical purposes. It is necessary to go beyond the immediate experience of sense perception, and to grasp the general processes, laws and hidden relations which lie beyond frequently deceptive appearance.
Ordinary human thought prefers to cling to what is concrete and familiar. It is easier to accept what is apparently fixed and well known rather than new ideas which challenge what is familiar and customary. Routine, tradition, custom and social convention represent a powerful force in society, akin to the force of inertia in mechanics. In normal periods most people are reluctant to question the society in which they live, its morality, ideology and property forms. All kind of prejudices, political ideas, "scientific" orthodoxy are accepted uncritically, until some profound change in people’s life force them to question what is.
Social and intellectual conformism is the commonest form of self deception. Familiar ideas are taken to be correct just because they are familiar. Thus, the notion that private property, money and the bourgeois family are eternal and unchanging features of life has sunk deeply into the popular consciousness, although it bares no relation whatsoever to the truth. Dialectics is the direct opposite of this superficial and commonplace way of thinking. Precisely because it challenges familiar ideas, it frequently arouses fierce opposition. How is it possible, to challenge the law of identity, which states what seems obvious, that "A equals A"? This so-called law is the logical reflection of a popular prejudice, that everything is what it is, and nothing else; that nothing changes. Dialectics, on the contrary, sets out from the opposite point of view, that everything changes, comes into being and passes away.
The empiricist thinker, who claims to take things "as they are," imagines himself to be very practical and concrete. But, in reality, things are not always what they seem to be, and frequently turn out to be their opposite. This kind of immediate sensuous knowledge is the lowest kind of knowledge, like that of a baby. A really scientific understanding of reality requires us to break down the information provided by sense perception in order to get at the true nature of the things under consideration. A deeper analysis always reveals the contradictory tendencies which underlie even the most apparently fixed, solid, and immutable things, which eventually will lead to them being transform into their opposites. It is precisely these contradictions which are the source of all life, movement and development throughout nature. In order to get a real understanding, it is necessary to take things, not just as they are, but also as they have been, and as they necessarily will become.
For simple everyday purposes, formal logic and "common sense" is sufficient. But beyond certain limits it no longer applies. At this point dialectics become absolutely essential. Unlike formal logic, which cannot grasp contradictions and seeks to eliminate them, dialectics represents the logic of contradiction, which is a fundamental aspect of nature and thought. By a process of analysis, dialectics reveals these contradictions and shows how they are resolved. However, new contradictions always appear, thus giving rise to a never-ending spiral of development. This process can be seen in the entire development of science and philosophy, which takes place through contradictions. This is not an accident. It reflects the nature of human knowledge as an infinite process in which the solution of one problem immediately give rise to new ones, which are in turn resolved, and so on ad infinitum.
If we set out from the most elementary form of knowledge at the level of sense-experience, the limitations of formal logic and "common sense" very soon become clear. The mind simply registers the facts as we find them. At first sight, the truths of sense perception seem to be simple and self evident. They can be confidently relied upon but on closer examination, things are not so simple. What appears to be solid and reliable turns out not to be so. The ground begins to shift beneath our feet.
Sense-certainty sets out from the "here" and the "now." Of this Hegel says: "Sense-certainty itself has thus to be asked: What is the This? If we take it in the two-fold form of its existence, as the Now and as the Here, the dialectic it has in it will take a form as intelligible as the This itself. To the question, What is the Now? we reply, for example, the Now is night-time. To test the truth of this certainty of sense, a simple experiment is all we need: write that truth down. A truth cannot lose anything by being written down, and just as little by our preserving and keeping it. If we look again at the truth we have written down, look at it now, at this noon-time, we shall have to say it has turned stale and become out of date." (Op. cit., p. 151.)
This comment of Hegel recalls the famous paradoxes of Zeno in relation to motion. For example, if we wish to fix the position of an arrow flying, to say where it is now, the moment that we point to it, it has already passed, and therefore the "now" is not something that is, but something that has been. Thus, what initially appear to be true, turns out to be false. The reason is to be found in the contradictory nature of movement itself. Movement is a process, not a collection of separate points. Similarly, time consists of an infinite number of "nows," all taken together. Likewise the "here" turns out to be not a single "here," but a before and a behind, and an above and a below, and a right and a left. What is here, as a tree, the next minute is here as a house, or something else.