What is the self? As with any complex and slippery concept, we can draw on literally thousands of years worth of philosophical discussions in both the eastern and western traditions to address the question. But perhaps it will be simpler to begin with two contrasting definitions from a dictionary:

In philosophy:

The ego; that which knows, remembers, desires, suffers, etc., as contrasted with that known, remembered, etc.

The uniting principle, as a soul, underlying all subjective experience.

Setting aside metaphysically questionable talk of "soul," it should be obvious that there is such thing as the self. We do "know, remember, desire, suffer, etc.," and we do have unified subjective experiences. Whatever turns out to make that possible is the self.

This, however, doesn't mean that the self is a stable entity, or a specific thing located somewhere inside our brain. Nor, certainly, is there any reason to believe that -- whatever it is -- it will survive our physical demise.

The most "skeptical" conception of the self in western literature is usually attributed to David Hume. In his A Treatise of Human Nature he famously wrote: "I may venture to affirm of the rest of mankind, that they are nothing but a bundle or collection of different perceptions, which succeed each other with inconceivable rapidity, and are in a perpetual flux and movement."

The Stoic take on what constitutes the self is eminently practical and - when properly understood - can dramatically change our life.

This turns out to be analogous to the oft-mentioned Buddhist notion of anatta, or no-self. Contra popular understanding, however, this is not a statement that there is no self, but more precisely that there are no essential or unchanging things that constitute our selves.

By contrast, the Stoics are often presented as putting forth an essential conception of the self. I do not think this is correct, as the Stoic notion is actually similar to the Buddhist one as well as the one put forth by Hume. Moreover, the Stoic take on what constitutes the self is eminently practical and -- when properly understood -- can dramatically change our life. For the better.

To explore the issue, let us consider two prominent figures that have shaped Stoic thinking and continue to do so: the Pre-Socratic philosopher Heraclitus, and the early second century Stoic philosopher Epictetus.

Heraclitus was a major influence on the Stoics, who imported into their philosophy a number of key elements from him. One such element is encapsulated by the Heraclitean dictum that "We never step into the same river twice." Why not? Because both the river and ourselves are never the same. This is because everything in the universe is a process, not a static thing. Even objects that appear to be static on a human timescale, such as mountains, are in fact a snapshot of a series of dynamic processes, such as tectonic movements and erosion.

The Stoic philosopher-emperor Marcus Aurelius often deployed Heraclitean metaphysics in his Meditations, drawing out its ethical implications: "Acquire the contemplative way of seeing how all things change into one another, and constantly attend to it, and exercise yourself about this part of philosophy. For nothing is so much adapted to produce magnanimity." Contemplating the impermanence of everything, including our own self, leads to magnanimity, literally "greatness of soul," because one is less likely to be attached to specific configurations of events and more likely to accept change as an inherent and necessary aspect of how the cosmos works. Buddhists would nod approvingly.