Thales (followed by other Monists, such as Anaximander, Anaximenes, Heraclitus, Parmenides) proposed that nature can be explained by reference to a single unitary principle that pervades everything. Numerous ancient Greek philosophers, including Xenophanes of Colophon and Antisthenes believed in a similar polytheistic monism that bore some similarities to monotheism. The first known reference to a unitary God is Plato's Demiurge (divine Craftsman), followed by Aristotle's unmoved mover, both of which would profoundly influence Jewish and Christian theology. Post-exilic Judaism was the first religion to conceive the notion of a personal monotheistic God within a monist context. The concept of ethical monotheism, which holds that morality stems from God alone and that its laws are unchanging, first occurred in Judaism, but is now a core tenet of most modern monotheistic religions, including Zoroastrianism, Christianity, Islam, Sikhism, and Baháʼí Faith.