It’s an error you see a lot these days: the use of bias in place of biased. Bias is a noun. You can have a bias, show a bias, or worry about bias. But when used as an adjective to describe something, the word is biased. It’s incorrect to say, “your opinion is bias,” “that’s a bias statement,” or “don’t be so bias.”
There are a number of factors that make this mistake likely and even hint at the notion that one day it could stop being seen as a mistake. First, in speech people drop the d or t sound from the end of words so often that linguists have a label for the phenomenon: "t/d deletion." Think about how you say “I passed through.” If you think very carefully about it, and speak very slowly you can get all the sounds in there, but in casual speech, it will come out as “I pass through.”
If a sound is often missing in speech, it’s likely to get left off in writing, too. There are a number of common errors where the –ed ending is left off of adjective forms. You see stain glass for stained glass, can goods for canned goods, bake chicken for baked chicken, and hundreds more like these (especially on menus).
When an adjective-noun phrase is used often enough, the –ed may eventually go missing for good. Skim milk, popcorn, and ice tea began their lives as skimmed milk, popped corn, and iced tea. Whip cream is well on its way to crossing over. Do you go over things with a fine-toothed comb or a fine-tooth comb? Either way works.
The process for biased losing its ending doesn’t quite fit this pattern. It doesn’t participate in any set phrases with a following noun of the skimmed milk variety (the most common words that follow biased are the prepositions against and toward). But bias fits another pattern: many adjectives that describe stances toward the world end in –ous, among them jealous, oblivious, righteous, serious, cautious, meticulous, treacherous, generous, callous, and pious. Bias might get a boost from the –ous family of adjectives because it ends in the same sequence of sounds.
Bias wouldn’t be the first such word to become an adjective because it coincidentally sounded like one. That’s what happened to the word genius, which has nothing to do with the –ous ending and was not used as an adjective until the 1920s, when people started saying things like “What a genius idea!” There are other words that coincidentally sound like they end in –ous, like prejudice and jaundice, which also seem especially susceptible to word errors of the bias type. “Are you prejudice?” gets thousands of hits on Google. “He was jaundice” and “She was jaundice” get thousands more.
Bias, prejudice, and jaundice are less likely than genius to become fully acceptable as adjectives because their spellings don’t fit as closely with the expectations for –ous words. They are still errors. But they are errors that reveal a complex sensitivity to the patterns of English. You might say the language is biased toward them.
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