/ˈbaɪəs/
[noun] A tendency to lean in a particular direction, favouring one side over another in a way that is often unfair or based on personal feelings rather than facts.
Before it meant prejudice, 'bias' was a sewing term — the diagonal cut across a piece of fabric.
The word 'bias' arrives in English in the early 16th century from Old French 'biais', meaning a slant or diagonal line. Its ultimate origin is debated — some trace it to Old Provençal 'biais', meaning oblique or sideways, and others point further back to a possible Greek root 'epikarsios', meaning athwart or crosswise. What is clear is that from its very earliest life in European languages, 'bias' carried the physical idea of something running at an angle, cutting across the expected straight line.
In its first English appearances, the word was thoroughly practical. Tailors and seamstresses used it to describe the diagonal direction of a woven fabric — cutting cloth 'on the bias' meant slicing across the grain at a 45-degree angle, which gave garments more stretch, drape, and elegance. This was skilled work, and the bias cut became a hallmark of fine dressmaking. The great French designer Madeleine Vionnet later made the bias cut famous in the 1920s and 30s, though the term itself had been in the tailor's vocabulary for centuries before her.
From the world of cloth, 'bias' migrated into the world of bowls — the popular green-lawn game played across Britain and Europe. In bowls, the balls themselves were not perfectly spherical; they were weighted or shaped slightly off-centre so that they curved as they rolled across the green. This built-in lean was called the ball's 'bias'. By the mid-16th century, the word had made this hop from fabric to sport, carrying with it the same essential idea: something that pulls or curves away from a straight, neutral path.
The leap from lawn bowling to human psychology was short and inevitable. By the late 16th and early 17th centuries, English writers were using 'bias' to describe the invisible weights inside a person's mind — the predispositions, preferences, and prejudices that cause their judgements to curve away from perfect neutrality. Francis Bacon, one of the great thinkers of the era, wrote with forensic precision about the way the human intellect is warped by its 'biases', which he saw as a fundamental problem for the pursuit of true knowledge. His work helped cement the psychological sense of the word.
What makes the word's journey so compelling is how perfectly the original image survives inside the abstract meaning. When we say someone has a bias, we are still saying, in the language of 16th-century tailors and bowlers, that they do not run straight. Their thinking cuts at an angle. There is a diagonal in them, a curve built into how they roll. The metaphor never needed replacing because it was never really a metaphor — it was always just a physical truth about the nature of things that lean.
In modern usage, 'bias' has expanded enormously, sprawling across disciplines from statistics and journalism to artificial intelligence and neuroscience. We now speak of cognitive bias, algorithmic bias, confirmation bias, and unconscious bias. The word has become one of the central diagnostic terms of contemporary intellectual life, a way of naming the invisible tilts in our systems and our selves. Yet every time it is used, no matter how technical the context, it carries in its bones the memory of a weighted bowling ball curving gently across a sunlit English green.