I think that both
essentialism and
constructivismand different than
solipsism, for the following reasons:
Essentialism is based on the
idea that some concepts (
forms would probably be the best word, as used by
Plato) are immutable and unchanging, and do not depend on the subjective judgement of indviduals. This means that these concepts must exist separately from any given individual consciousness (or at least any individual mortal consciousness; theologians of the pre-
Modernist era often used the theoretical existence of an absolute, essentialist good as the basis for proving the existence of
God.) So, obviously
essentialism is incompatible with
solipsism.
However, it does not neccesarily follow that
constructivism is compatible with
solipsism.
Constructivism as a
philosophy dictates that the perception of such qualities as
good and
evil is
socially constructed; in other words, that the perception you hold is shaped by other people. This, too, is incompatible with
solipsism, because it requires that other people exist independantly of yourself, and that you are capable of importing new information from these outside sources in forming your judgements.
I think the major point of difference between
solipsism and
constructivism is that
constructivism attempts to refute the existence of an empirical
astract reality, while solipsism attempts to refute the existence of an empirical
concrete reality.