Realism is the philosophical school of thought that asserts that the external world exists independently of our minds. It is opposed to idealism, which asserts that the external world is dependent on our minds.

Skepticism is the philosophical school of thought that asserts that the external world is unknowable. It is opposed to realism, which asserts that the external world is knowable.

Phenomenalism is the philosophical school of thought that asserts that the external world is composed of sense data. It is opposed to realism, which asserts that the external world is composed of physical objects.

Plato argued that the external world is a collection of ideas. He believed that the physical world is a mere shadow of the real world, which is the world of ideas.

Aristotle argued that the external world is composed of physical objects. He believed that the physical world is the only real world and that the world of ideas is a mere abstraction.

Locke argued that the external world is composed of sense data. He believed that the physical world is a collection of qualities that are perceived by our senses.

Hume argued that the external world is unknowable. He believed that we can only know our own ideas and that we cannot know anything about the external world.

Leibniz argued that the external world is a collection of substances. He believed that substances are the basic building blocks of the universe and that they are characterized by their properties.

Leibniz argued that the external world is a collection of monads. He believed that monads are simple, indivisible substances that are the basic building blocks of the universe.

Whitehead argued that the external world is a collection of events. He believed that events are the basic building blocks of the universe and that they are characterized by their relationships to each other.

Bergson argued that the external world is a collection of processes. He believed that processes are the basic building blocks of the universe and that they are characterized by their continuity and change.

Einstein argued that the external world is a collection of fields. He believed that fields are the basic building blocks of the universe and that they are characterized by their properties.

Wheeler argued that the external world is a collection of information. He believed that information is the basic building block of the universe and that it is characterized by its patterns and relationships.

Everett argued that the external world is a collection of quantum states. He believed that quantum states are the basic building blocks of the universe and that they are characterized by their probabilities.

Hawking argued that the external world is a collection of virtual particles. He believed that virtual particles are the basic building blocks of the universe and that they are characterized by their energy and momentum.