“Logical empiricism holds the view, notwithstanding some its assertions, that the forms of knowledge and consequently the relations of man to nature and to other men never change. According to rationalism, too, all subjective and objective potentialities are rooted in insights which the individual already possesses, but rationality uses existing objects as well as the active inner striving and ideas of man to construct standards for the future. In this regard, it is not so closely associated with the present order as is empiricism.”

Human Nature and Social Theory (1969)
Context: What about the utopian thinkers of all ages, from the Prophets who had a vision of eternal peace, on through the Utopians of the Renaissance, etc.? Were they just dreamers? Or were they so deeply aware of new possibilities, of the changeability of social conditions, that they could visualize an entirely new form of social existence even though these new forms, as such, were not even potentially given in their own society? It is true that Marx wrote a great deal against utopian socialism, and so the term has a bad odor for many Marxists. But he is polemical against certain socialist schools which were, indeed, inferior to his system because of their lack of realism. In fact, I would say the less realistic basis for a vision of the uncrippled man and of a free society there is, the more is Utopia the only legitimate form of expressing hope. But they are not trans-historical as, for instance, is the Christian idea of the Last Judgment, etc. They are historical, but the product of rational imagination, rooted in an experience of what man is capable of and in a clear insight into the transitory character of previous and existing society.

Source: Against Method (1975), p. 223.

Source: One-Dimensional Man (1964), pp. 137-138

Concluding Paragraph
On Practice (1937)
Original: (zh-CN) 通过实践而发现真理，又通过实践而证实真理和发展真理。从感性认识而能动地发展到理性认识，又从理性认识而能动地指导革命实践，改造主观世界和客观世界。实践、认识、再实践、再认识，这种形式，循环往复以至无穷，而实践和认识之每一循环的内容，都比较地进到了高一级的程度。这就是辩证唯物论的全部认识论，这就是辩证唯物论的知行统一观。

Source: The Art of Loving (1956)
Context: To speak of love is not "preaching," for the simple reason that it means to speak of the ultimate and real need of every human being. That this need has been obscured does not mean it does not exist. To analyze the nature of love is to discover its general absence today and to criticize the social conditions which are responsible for this absence. To have faith in the possibility of love as a social and not only exceptional-individual phenomenon, is a rational faith based on the insight into the very nature of man.

Source: Personal Knowledge (1958), p. 17

Source: The Anatomy of Human Destructiveness (1973), p. 483
Context: Optimism is an alienated form of faith, pessimism an alienated form of despair. If one truly responds to man and his future, ie, concernedly and "responsibly." one can respond only by faith or by despair. Rational faith as well as rational despair are based on the most thorough, critical knowledge of all the factors that are relevant for the survival of man.

Sir Harry Johnston Liberia (1906), vol. 1, p. 257.
Criticism of The Martyrdom of Man

Ideology and Utopia (1929)
Context: This first non-evaluative insight into history does not inevitably lead to relativism, but rather to relationism. Knowledge, as seen in the light of the total conception of ideology, is by no means an illusory experience, for ideology in its relational concept is not at all identical with illusion. Knowledge arising out of our experience in actual life situations, though not absolute, is knowledge none the less. The norms arising out of such actual life situations do not exist in a social vacuum, but are effective as real sanctions for conduct. Relationism signifies merely that all of the elements of meaning in a given situation have reference to one another and derive their significance from this reciprocal interrelationship in a given frame of thought. Such a system of meanings is possible and valid only in a given type of historical existence, to which, for a time, it furnishes appropriate expression. When the social situation changes, the system of norms to which it had previously given birth ceases to be in harmony with it. The same estrangement goes on with reference to knowledge and to the historical perspective. All knowledge is oriented toward some object and is influenced in its approach by the nature of the object with which it is pre-occupied. But the mode of approach to the object to be known is dependent upon the nature of the knower.