/ˈbeɪsɪs/
[noun] The main idea, fact, or principle that something is built on or developed from. It can also mean the starting point or reason for doing something.
Every time you say 'basis,' you are literally talking about a foot taking a step — the word comes from the Greek word for walking.
The word 'basis' travels to us almost unchanged from ancient Greek, where 'basis' (βάσις) meant 'a step,' 'a pedestal,' or 'the base on which something stands.' This Greek word came from the verb 'bainein' (βαίνειν), meaning 'to go' or 'to step.' So at its very heart, 'basis' is about movement — the act of a foot pressing down onto the ground. The image is beautifully physical: a single step, the point where a body meets the earth and weight is transferred.
The Greeks extended this meaning quite naturally from the literal to the abstract. Just as a column rests on its base, an argument or idea could rest on a 'basis' — a foundational point that supports everything above it. Greek philosophers, including Aristotle, used the word in logical and mathematical discussions to describe the foundational premise from which reasoning proceeds. The foot-step became, by metaphor, the first intellectual step in any line of thought.
Latin absorbed the word directly from Greek, keeping both its spelling and its meaning almost perfectly intact. Latin 'basis' referred to the base or foundation of a structure, and Roman writers used it in architectural, philosophical, and rhetorical contexts. The Latin form was so clean and direct that it required almost no adaptation. This is why 'basis' looks and sounds so different from most English words with Latin roots — it was borrowed wholesale rather than worn down through centuries of everyday speech.
English picked up 'basis' in the late 16th century, primarily through scholarly and scientific writing that drew heavily on Latin texts. At first it appeared most often in technical or philosophical writing, where writers needed a precise word for a foundational principle or underlying assumption. Over the following two centuries it settled into broader use, appearing in legal, political, and everyday contexts. Phrases like 'on the basis of' and 'on a daily basis' show how the word moved from the library into ordinary conversation.
What makes 'basis' especially interesting is the family of English words it belongs to. The same Greek root 'bainein' — to step or go — feeds into a surprising number of everyday words. Greek 'basis' → Latin 'basis' → English 'base' and 'basis.' The Greek 'anabainein' (to go up) gave us 'acrobat' through a different branch, while the root also connects to 'diabetes,' which in Greek literally described a person who 'steps across' or passes liquid through the body. Even 'come' in its ancient Indo-European ancestor shares a distant family connection, since the Proto-Indo-European root *gʷem- meaning 'to go' or 'to step' underlies both the Greek 'bainein' and the Germanic ancestors of the English word 'come.' A single step taken in ancient Greece echoes through thousands of years of human language.