Editing Reality (section)

=== Time and space ===
{{Main|Philosophy of space and time}}

A traditional realist position in ontology is that time and space have existence apart from the human mind. [[Idealism|Idealists]] deny or doubt the existence of objects independent of the mind. Some [[anti-realism|anti-realists]] whose ontological position is that objects outside the mind do exist, nevertheless doubt the independent existence of time and space.

[[Immanuel Kant|Kant]], in the ''[[Critique of Pure Reason]]'', described time as an ''[[A priori and a posteriori|a priori]]'' notion that, together with other ''a priori'' notions such as [[space]], allows us to comprehend [[empirical evidence|sense experience]]. Kant denies that either space or time are [[Substance theory|substance]], entities in themselves, or learned by experience; he holds rather that both are elements of a systematic framework we use to structure our experience. Spatial [[measurement]]s are used to [[quantity|quantify]] how far apart [[Physical body|objects]] are, and temporal measurements are used to quantitatively compare the interval between (or duration of) [[Spacetime#Basic concepts|events]]. Although space and time are held to be ''transcendentally ideal'' in this sense, they are also ''empirically real'', i.e. not mere illusions.

Idealist writers such as [[J. M. E. McTaggart]] in ''[[The Unreality of Time]]'' have argued that time is an illusion.

As well as differing about the reality of time as a whole, metaphysical theories of time can differ in their ascriptions of reality to the [[past]], present and [[future]] separately.
* [[Presentism (philosophy of time)|Presentism]] holds that the past and future are unreal, and only an ever-changing present is real.
* The [[block universe]] theory, also known as Eternalism, holds that past, present and future are all real, but the passage of time is an illusion. It is often said to have a scientific basis in [[Theory of relativity|relativity]].
* The [[growing block universe]] theory holds that past and present are real, but the future is not.

Time, and the related concepts of process and [[evolution]] are central to the [[system-building metaphysics]] of [[A. N. Whitehead]] and [[Charles Hartshorne]].