Time is a part of the measuring system
Measurement is the process or the result of determining the ratio of a physical quantity, such as a length, time, temperature etc., to a unit of measurement, such as the metre, second or degree Celsius...

 used to sequence
In mathematics, a sequence is an ordered list of objects . Like a set, it contains members , and the number of terms is called the length of the sequence. Unlike a set, order matters, and exactly the same elements can appear multiple times at different positions in the sequence...

 events, to compare the durations of events
Event (philosophy)
In philosophy, events are objects in time or instantiations of properties in objects. However, a definite definition has not been reached, as multiple theories exist concerning events.-Kim’s Property-Exemplification Account of Events:...

 and the intervals between them, and to quantify
Quantification has several distinct senses. In mathematics and empirical science, it is the act of counting and measuring that maps human sense observations and experiences into members of some set of numbers. Quantification in this sense is fundamental to the scientific method.In logic,...

 rates of change such as the motions
Motion (physics)
In physics, motion is a change in position of an object with respect to time. Change in action is the result of an unbalanced force. Motion is typically described in terms of velocity, acceleration, displacement and time . An object's velocity cannot change unless it is acted upon by a force, as...

 of objects
Physical body
In physics, a physical body or physical object is a collection of masses, taken to be one...

The temporal position of events with respect to the transitory present
Present is a time that is neither past nor future.Present may also refer to:- Time and timing :* Present tense, the grammatical tense of a verb* Before Present, radiocarbon dates relative to AD 1950* Presenting, a medical term* Presenteeism...

 is continually changing; events happen, then are located further and further in the past
Most generally, the past is a term used to indicate the totality of events which occurred before a given point in time. The past is contrasted with and defined by the present and the future. The concept of the past is derived from the linear fashion in which human observers experience time, and is...

Time has been a major subject of religion
Religion is a collection of cultural systems, belief systems, and worldviews that establishes symbols that relate humanity to spirituality and, sometimes, to moral values. Many religions have narratives, symbols, traditions and sacred histories that are intended to give meaning to life or to...

, philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

, and science
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...

, but defining it in a non-controversial manner applicable to all fields of study has consistently eluded the greatest scholars.

Time is an illusion, lunchtime doubly so.

Douglas Adams, The Hitchhiker's Guide to the Galaxy

How can I tell that the past isn't a fiction designed to account for the discrepancy between my immediate physical sensations and my state of mind?

The man in the shack, in The Restaurant at the End of the Universe|The Restaurant at the End of the Universe (1980) by Douglas Adams. Ch. 29

Time is not a reality [hupostasis], but a concept [noêma] or a measure [metron]…

Antiphon (person)|Antiphon the Sophist, Truth

Time is not bought ready-made at the watchmaker's.

Jacob Bronowski, Science and Human Values (1956)

With the magnificence of eternity before us, let time, with all its fluctuations, dwindle into its own littleness.

Thomas Chalmers, reported in Josiah Hotchkiss Gilbert, Dictionary of Burning Words of Brilliant Writers (1895), p. 584.

In the spirit of faith let us begin each day, and we shall be sure to " redeem the time " which it brings to us, by changing it into something definite and eternal. There is a deep meaning in this phrase of the apostle, to redeem time. We redeem time, and do not merely use it. We transform it into eternity by living it aright.

James Freeman Clarke, reported in Josiah Hotchkiss Gilbert, Dictionary of Burning Words of Brilliant Writers (1895), p. 583.

Time,— that black and narrow isthmus between two eternities.

Charles Caleb Colton, reported in Josiah Hotchkiss Gilbert, Dictionary of Burning Words of Brilliant Writers (1895), p. 582.

Time goes, you say? Ah no, alas, time stays, we go.

Henry Austin Dobson

The distinction between past, present, and future is only a stubbornly persistent illusion.

Albert Einstein

A butterflyFluttering over the vendor’sDry flowers of springOnly two days it fliesCaught by the lost boyYet still.

For Peng Fajardo by Shane Castro in The Now