What Is Existence, And How Can Humans Know They Exist?

Humans believe they exist through a foundational philosophical insight often traced to René Descartes’ famous principle, “cogito ergo sum” (”I think, therefore I am.”) This “certainty” arises from a process of radical doubt, where one systematically questions everything that can be doubted to find an “unshakable truth.”

Descartes’ method, called Methodical Doubt, involves doubting sensory experiences, which can deceive us, like in dreams or illusions, mathematical truths, and even the external world, which an all-powerful deceiver might falsify. In this hyperbolic skepticism, everything seems uncertain, except the act of doubting, itself. 

To doubt requires cogitation, and thinking presupposes a thinker who must exist. As Descartes puts it in his Meditations on First Philosophy, even if a malicious “evil genius” deceives me about everything else, the deception still demands that I, the thinking subject, exist at the moment of my cogitation. Thus, “I am, I exist” is necessarily true whenever it is conceived or asserted.

This isn’t just logical wordplay; it’s a self-evident intuition, immune to further doubt because denying it affirms the very thinking that enables the denial. It’s present-tense and first-person: as long as you’re aware, (doubting, affirming, sensing, or willing), you exist as a “thinking thing.” 

This provides absolute "certainty" of self-existence, serving as the bedrock for further knowledge. Philosophers debate whether it proves a substantial “self” or just momentary awareness, but it remains the most direct way humans access "indubitable proof" of their own being.

Existence, in philosophy, is the state of Being or Actuality. Fundamentally, what it means for something to be, rather than merely be conceivable as existing. It’s the core subject of ontology, the branch of metaphysics studying the nature of Being, (the categories of what exists, and the features all entities share.) 

Ontology asks: What counts as real? How do things come to be, persist, or cease? A key distinction is between being (broadly, inclusion in reality or discourse, like fictional characters that “are” in stories), and actually existing, (referring to concrete, actual individuals in the world). 

Aristotle saw existence as identical to a thing’s essence, (what it is), so a human simply is human, with no extra “stamp” of existence. Thomas Aquinas separated them: Essence is what a thing could be (e.g., the idea of a unicorn), while Existence is the act of Being, that added to Essence makes it real. 

How do we make sense of “unicorns don’t really exist” without implying unicorns may somewhat exist in a person’s mind? Logicians like Bertrand Russell treat existence as a second-order property: “Unicorns exist” means the concept of unicorn is instantiated by at least one thing, (which it’s not). 

Immanuel Kant argued existence isn’t a property at all; it doesn’t add to a concept. Saying “God exists” doesn’t enhance the idea of God any more than “real dollars exist” except actually seeing real dollars adds value beyond the concept of an unseen, unknown God. 

Major debates include ontological arguments: Anselm of Canterbury claimed God’s existence follows from the concept of God as the greatest conceivable being. Non-existence would make God less great, which is a contradiction. Kant critiqued this, insisting existence can’t be “proven” from concepts alone.

Thinkers like Alexius Meinong allowed for “objects” that subsist in thought but lack existence (e.g., Sherlock Holmes “is” a detective but doesn’t exist). Critics avoid this to prevent paradoxes, like infinite contradictory entities. A person who has never actually been to Australia can still have faith that it is there, understanding that Faith is the Hope that what is believed is Real.

Ultimately, existence is contingent on things beginning and ending, yet the concept of existence is elusive. Only existing things have attributes,  (something as being caused by someone or something.) It’s not just “being there,” but the actuality that makes reality possible. That said, Existence continues to be debated across traditions from Aristotle to modern modal logic.

Existence my make one feel in the same way a dream feels real until you wake up. But betting your life on it feels like overkill. The Illusion Hypothesis explains anomalies but doesn’t predict or falsify anything useful. 

Philosophical questions of existence may be more poetry than proof. However, if existence is simply mind-fluff, maybe we’re all just stumbling our way through "life' seeking the code. What do you think, are you dreaming or awake?