reduction

The general sense that every specialist meaning narrows. The word comes from Middle English reduccion, through Old French from Latin reductiō, and is built like reduce plus -tion. It names the act and its outcome alike, so it can be counted: reductions are made in schedules, costs or emissions. The preposition that usually follows is in, and it marks whatever shrank.

As a quantity, the word takes a number: a 5% reduction in robberies. The two prepositions do different jobs. In names what fell, while of introduces the size of the cut, as in a reduction of two hundred jobs. Keeping them apart avoids the muddle of a reduction of robberies, which reads as if the robberies themselves were the amount removed.

Chemistry measures this change in charge. A substance that gains electrons has its oxidation state lowered, so it is said to be reduced. A reduction never happens alone, because every one is paired with an oxidation. Loss of oxygen and gain of hydrogen are the familiar signs, but electron gain is the rule that covers every case.

In the kitchen the word names both the technique and its result. You reduce a stock, and what is left in the pan is a reduction, as in a balsamic reduction. Fast boiling drives off water, so the flavor concentrates and the liquid thickens. On a menu the word names the finished sauce or glaze, not the cooking step.

This is a matter of form, not value: the expression after reduction is equal to the one before, only simpler. Canceling common factors and combining like terms are the standard moves. The verb takes to, so a fraction is reduced to lowest terms. The noun follows the same pattern, as in the reduction of a fraction to three-fifths.

In medicine, reducing means putting back, not making smaller: the bone or joint returns to where it belongs. Doctors distinguish closed reduction, done by manipulation without opening the skin, from open reduction, which exposes the bone surgically. Open reduction often appears in the set phrase open reduction and internal fixation. Its technical synonym is taxis.

Complexity theory uses this sense to compare difficulty. If every instance of one problem can be turned into an instance of another, solving the second solves the first. Direction matters: hardness proofs reduce from a known hard problem to the new one. A polynomial-time reduction adds a condition, because the transformation itself must run efficiently.

Musicians use this word for a working score rather than a new composition. Most often it is a piano reduction, which squeezes an orchestral or operatic texture onto one keyboard. That lets a single player rehearse the whole work, or a conductor study it before meeting the full forces. The compound with the instrument's name is the usual way to say it.

Phenomenology's term of art is closely tied to Husserl. The reduction brackets, or suspends, the question of whether objects exist outside the mind. What remains to describe is how they appear to consciousness. In full it is the phenomenological reduction, and in philosophical writing the bare word usually stands for that longer phrase.

Metalworkers state this sense as a percentage. Gordon L. Robertson's Food Packaging Principles and Practice (2016) describes a 90% reduction by cold rolling, taking sheet from about 2 mm to under 0.2 mm. Because the figure compares the thinning with the original thickness, it rises as the material gets thinner. It often appears in the compound thickness reduction.

This sense names a colonial institution and now belongs to historical writing. Missionaries, among them Jesuits, gathered local people into planned settlements for instruction and conversion. The word keeps its Spanish and Portuguese setting and often carries a place or nation with it, as in Spanish reductions in Mexico. A modern reader should not take it to mean any kind of decrease.