"Does that star really exist?"
Haru pointed at the night sky.
"We see it, so it exists," Ren answered.
"But it might be light from hundreds of years ago. Maybe it's already gone."
Simon joined from the side. "So past stars don't exist?"
Haru thought. "It's difficult. What makes something 'exist'?"
Ren organized. "Existence has at least two meanings. Physical existence and conceptual existence."
"Conceptual existence?"
"Numbers don't physically exist, but exist as concepts."
Simon gave examples. "Justice, love, friendship. All conceptual existences."
"So concepts don't really exist?" Haru asked.
"Depends on the definition of reality," Ren answered carefully. "If only what occupies physical space is real, concepts aren't real."
"But concepts have influence," Simon said. "People die for love. A powerful existence."
"Things with causal power are real?" Haru proposed.
Ren nodded. "One definition. But then what about dreams? Dreams also affect behavior."
"Do dreams exist?"
"Subjectively they exist. Objectively, they exist as brain activity."
Simon approached from another angle. "Descartes said 'I think, therefore I am.'"
"Thought proves existence?" Haru showed interest.
"The act of doubting itself demonstrates the doubter's existence. That much is certain."
Ren supplemented. "But that's only self-existence. Others and the external world aren't proven yet."
"So maybe nothing exists except me?" Haru was surprised.
"Solipsism," Simon named it. "Other minds are unprovable."
"But we have to believe," Ren said. "Practically speaking."
Haru asked. "So believing in existence and existing are different?"
"Philosophically, very different," Ren acknowledged.
Simon added. "Kant said existence isn't a predicate."
"Not a predicate?"
"'God is omnipotent' is God's property. But 'God exists' isn't a property. Existence is a different dimension."
Haru was confused. "Then what is it?"
Ren explained. "Existence is a concept being instantiated. The concept 'unicorn' exists, but has no instances."
"Without instances, it doesn't exist?"
"Not physically. But as a concept, it exists."
Simon looked out the window. "In quantum mechanics, existence isn't determined until observed."
"Observation creates existence?" Haru was surprised.
"In some interpretations, yes. But it's debated."
Ren organized. "Existence has various layers. Material, conceptual, potential."
"Potential?"
"Not yet realized, but exists as possibility. Like tomorrow's self."
Haru thought deeply. "So everything both exists and doesn't exist."
"Depends on context," Simon said. "The answer changes based on what we're talking about."
Ren said quietly. "The question of existence is also a question of language. How we define 'exist' determines the answer."
"So there's no answer?" Haru sounded a bit disappointed.
"No single answer," Ren acknowledged. "But asking deepens understanding."
Simon smiled. "Ontology is an endless dialogue."
Haru looked up at the night sky again. "That star definitely exists in my mind."
"That's also a truth," Ren said.
The three quietly gazed at the stars. Existence is ambiguous and can't be fully grasped. Still, there was meaning in continuing to ask.