Counting
Inclusive counting

Inclusive/exclusive counting are terms used for counting intervals. For inclusive counting the starting point is one; for exclusive counting the starting point is zero. Inclusive counting is usually encountered when dealing with time in Roman calendars and the Romance languages. In the ancient Roman calendar, the nones (meaning "nine") is 8 days before the ides; more generally, dates are specified as inclusively counted days up to the next named day. In the Christian liturgical calendar, Quinquagesima (meaning 50) is 49 days before Easter Sunday. When counting "inclusively", the Sunday (the start day) will be day 1 and therefore the following Sunday will be the eighth day. For example, the French phrase for " fortnight " is quinzaine (15), and similar words are present in Greek (δεκαπενθήμερο, dekapenthímero), Spanish (quincena) and Portuguese (quinzena). In contrast, the English word "fortnight" itself derives from "a fourteen-night", as the archaic " sennight " does from "a seven-night"; the English words are not examples of inclusive counting. In exclusive counting languages such as English, when counting eight days "from Sunday", Monday will be day 1, Tuesday day 2, and the following Monday will be the eighth day. For many years it was a standard practice in English law for the phrase "from a date" to mean "beginning on the day after that date": this practice is now deprecated because of the high risk of misunderstanding.

Similar counting is involved in East Asian age reckoning, in which newborns are considered to be 1 at birth.

Musical terminology also uses inclusive counting of intervals between notes of the standard scale: going up one note is a second interval, going up two notes is a third interval, etc., and going up seven notes is an octave.
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