Heraclitus was nicknamed "the Obscure" and lived in the city of Ephesus around 500 BCE. He believed that fire is the eternal, primordial substance from which everything is made. He believed in fate and a theory where a force of strife causes the combining of opposites, both ultimately being made of fire, which would result in more complex harmonies, creating unities. He also believed in a system of justice that ensured the balance between opposites. He believed that nature is unclear to us and that we must expect the unexpected in order to find it. He is most famous for his doctrine that everything is always in a constant flux. One of his more famous quotations is “You cannot step twice into the same river.” He believed in an afterlife and that Zeus is the greatest in wisdom, beauty, and everything else, and that everything in the world is just and fair to the gods, though men suppose some things just and some things unjust through lack of trust.
There are many problems with knowing what Heraclitus's philosophy was. First of all, only a relatively small number of fragments remain that deal with Heraclitus's thoughts, so we only get a small glimpse of his thought and we don't have a context for understanding them. Second of all, the fragments we have were recorded by other writers, which may or may not be apocryphal or accurate. Finally, Heraclitus supposedly wrote his philosophy in cryptic poetic lines, so it would have been difficult to understand what he meant exactly even in better conditions. Heraclitus is somewhat skeptical. For him, knowledge is only acquired through the senses and critical thinking about the information of the senses. From this fact one can easily see why he comes to many of his philosophical conclusions. Metaphysically speaking, he believes that everything is essentially one and the same. He says that fire is this same one essence of everything, but his use of fire here may just be an appropriate metaphor for describing reality, to wit, that everything is in constant flux and change, just like fire. From moment to moment, in one sense a thing is what it was before, but in another sense it has changed and is no longer what it was. This constant change occurs with everything, so that all things are constantly new and different, but even what was the same in any one thing will change eventually, and so all things will completely cease to exist. I find contradicting fragments on his believing in an afterlife. He also asserts that all things also have elements of their opposites within them, and the same is true for actions. Indeed, he states that many things can only exist with the mutual existence of their opposites, and often times an action actually is its opposite in another sense and from another perspective. Also, seemingly opposite things will eventually change into each other, for example, earth changes into water, and water changes into earth. These morphings of the objects of the world often have a cyclical evolution that ends up where it began. The dissolution of everything in the flux and eventual recreation into their opposites comes about because all things are in continual strife, war, competition, and conflict with all other things, even down to the level of the elements; ultimately, this is necessary and results in overall balance and harmony, "the cosmos works by harmony of tensions". This is the situation we are in and we cannot escape from it. He believes all events are fated. He believes in the gods but criticizes idolotry, sacrifices, and certain religious rites and rituals. He emphasizes the relative perspectives of all beings for what is valued as good and bad, for example, what is valued as great by one person is foolish from another perspective. However, he very clearly believes that there is both an objective reality, an objective good and bad, and an objective justice. When judging mankind from the objective good, he sees mankind, in general, in a bad light, and thinks that those under the influence of alcohol are witless. And he encourages our keeping in mind the view of mankind from the superior perspective of the cosmic forces, which finds most of the things valued by mankind as foolish, petty, and base, "In everything we have attained the excellence of apes."