Dialectic

Broadly speaking, a dialectic is an exchange of propositions and
counter-propositions resulting in a synthesis of the opposing assertions or
at least a qualitative transformation of the direction of the dialogue.

In Philosophy

When using the word "dialectic" philosophers usually refer to either the
Socratic dialectical method of cross-examination, or to Hegel's dialectical
model of history.

Socratic Dialectic

In Plato's dialogues, Socrates typically "argues" by means of
cross-examining someone else's assertions in order to draw out the inherent
contradictions within the other's position. For example, in the Euthyphro,
Socrates asks Euthyphro to provide a definition of piety. Euthyphro replies
that the pious is that which is loved by the gods. But, Socrates points out,
the gods are quarrelsome and their quarrels, like human quarrels, concern
objects of love or hatred. Euthyphro consents that this is the case.
Therefore, Socrates reasons, at least one thing exists which certain gods
love but other gods hate. Again, Euthyphro consents. Socrates concludes that
if Euthyphro's definition of piety is true, then there must exist at least
one thing which is both pious and impious -- which, Euthyphro admits, is absurd.

Hegelian Dialectic

Although Hegel never used such a classification himself, Hegel's dialectic
is often described as consisting of three stages: a thesis, an antithesis
which contradicts or negates the thesis, and a synthesis embodying what is
essential to each. In the Logic, for instance, Hegel describes a dialectic
of existence: first, existence must be posited as pure Being (thesis); but
pure Being, upon examination, is found to be indistinguishable from Nothing
(antithesis); yet both Being and Nothing are united as Becoming (synthesis),
when it is realized that what is coming into being is, at the same time,
also returning to nothing (consider life: old organisms die as new organisms
are created or born). Like Socratic dialectic, Hegel's dialectic proceeds by
making implicit contradictions explicit: each stage of the process is the
product of contradictions inherent or implicit in the preceding stage. For
Hegel, the whole of western history is one tremendous dialectic, the largest
moments of which chart a progression from self-alienation as slavery to
self-unification and realization as the rational, constitutional state of
free and equal citizens.

Marxist Dialectic

Karl Marx and Friedrich Engels saw Hegel as "standing on his head", and put
him back on his feet, ridding Hegel's logic of its idealist orientation, and
conceiving what is now known as materialist or Marxist dialectics. The
dialectical approach to the study of history then gave rise to historical
materialism. Under Stalinism, Marxist dialectics developed into what was
called "diamat" (short for dialectical materialism), a system of thought
which some saw as becoming increasingly dogmatic and intellectually corrupt
due to the overpowering influence of its attendant political ideology.
Dialectical materialism is the chief philosophical basis behind the works of
Marx, Engels, Lenin, and Trotsky. Some Soviet academics, most notably Evald
Ilyenkov, did continue with philosophical studies of the dialectic free from
ideological bias, as did a number of thinkers in the West.