Arto and tendo

The terms arto (from the Latin verb artāre, meaning "compress" or "contract") and tendo (from the Latin verb tendere, meaning "stretch" or "extend") are two terms that are encountered in various capacities in microtonal theory as either independent words, or, as prefixes. Regardless of how they are encountered, the term "arto" means "contracted" while the term "tendo" means "stretched". When used as independent words, they tend to refer to concepts related to arto and tendo theory, however, when they are encountered as prefixes, they tend to describe the various types of neutral interval as in Alpharabian tuning, or else, the various types of major or minor interval that are in the small regions bounded by the common Pythagorean and Ptolemaic varieties of a given class, or tempered approximations thereof. It should be noted that arto and tendo theory predates the theory related to Alpharabian tuning.