1) Society and social structure
Modernism splits up society into classes and gives society a definite hierarchic structure, wiht a strong centered shape. Postmodernism gives and idea of a society that has gone beyond Post Colonialism and presents a fragmented and multicultural society, in which globalization and citizenship in the world are fundamental principles. In such society there are no points of reference.
2) Social roles
Modernism has got in its definition ideas of monopoly in economy and society, especially in politics. Totalitarism and monopolies are at the top of the hierarchies and control every aspect of man's life. Postmodernism refuses such "monopoly" because it considers it too oppressive and absolute , and purposes a decentered vision.
Modernism, since it has Enlightment among its anticipating movements, puts the subject and the individual quest at the centre of the universe. The individual is himslef object of quest and its psychology and behaviour is analyzed. On the other hand Postmodernism adopts a decentred subject, that isn't the centre of the universe but is part of the "whole". His actions are connected to their consequences on the world.
Modernism says that signifier and signifying are connected to form a strong semiotic unit, while Postmodernism says this isn't always true. Signifier and signifying crystalize knowledge and its fundations upside down. To achieve this goal Postmodernism uses the meaning of signifier and signifying.
In Modernism knowledge is essentially absolute and strongly monopolized: less people detain knowledge as a unique theory to which nobody can oppose. In Postmodernism there is a fragmented and local idea of knowledge, that shouldn't necessarily be summated to a universal one. Scientific clashes are strongly present in the scientific community, in according to a multi-angle prespective.
Modernism follows Newtonian physics and presents sciences like a thing you can't go against with any argumentation. Postmodernism follows Albert Einstein's theory of of relativity, in which things change according to the perspective you look at them. Postmodernism also follows quanum theories and the theory of strings (born in the 1960s), but there is a strong debate about time and space, especially about their ultimate nature: is it energy or what?
Modernism follows a linear causality in line with tradition, subdividing himself into Determinism and Finalism (much less present). Postmodernism adopts Konrad Lorenz's theory of chaos, in according to which a butterfly that flies in China causes a hurricane in the South of USA. Such theory is the result of complicated mathematic operantions and is still being debated in the scientific community.
8) Social change
Modernism follows mainly Charles Darwin's theory of evolution, that has got a linear route and was published in the last years of the 19th century. Postmodernism doens't totally follow such theory and purposes some alternative versions of the same thing, like the theories of deconstruction and reconstruction.