Hmm I think prejudice is kind of the judgement you make about a certain thing/person/group before knowing much about them. So for example if I got bitten by a dog as a child and then formed the opinion that all dogs are aggressive and will bite me, that is a prejudiced opinion (this is obviously untrue as not all dogs are like that). In more realistic cases, prejudices exist in terms of race, gender and sexuality. So a prejudice is usually a judgement made about something without actually knowing facts about it (and usually in a negative way). A bias is more to do with how you act. So if my friend and a stranger were having an argument, I would have a "bias" towards my friend because I know her already, so I would be more likely to support her than the stranger. So because I'm already friends with her, I would support her and my judgement would be "biased" and unfair. Another example is if I'm the CEO of a company and my friend and a stranger both applied to the job, with equal qualifications and experience, if I picked my friend I would be showing "bias" towards my friend as I favoured her and picked her over the stranger. I think the main difference is that a prejudiced opinion is usually negative and against a particular thing/group/person, but a bias is generally where you are favouring or supporting something/someone over someone else. Sorry if that didn't make much sense but they are very closely related words !

Paired together like that, in their meanings of "favorable or unfavorable attitudes toward a person," they're roughly synonyms. Sometimes it's helpful to go back to root meanings. "Bias" means "tilt" or "slant." "Prejudice" means "judged in advance." On that basis, we might say that a prejudice is harder, firmer, and allows no exceptions. "This boss has a bias against Martians (space aliens from the planet Mars). Non-Martians with 'good' performance get promotions, but only Martians with 'outstanding' performance get promotions." An example of prejudice would be a boss who says "No, don't bring this candidate for an interview. This candidate is a Martian. All Martians are inherently lazy, stupid, and ugly. There's no need to me to see if this Martian is diligent, smart, and handsome. I already know the answer."

Bias can used in a favorable or unfavorable context where prejudice is usually defined as just negative. Another way of looking at it is that prejudice is a form of bias, but bias is not always pre-judging or prejudicial. He prefers sweets over salty snacks so he's biased over cookies versus chips. - prejudice will not sound correct in this example. He doesn't like foreigners. He's prejudiced against them. - bias could work here, but prejudice has a stronger and more negative meaning. She prefers brown eyes to blue. - bias based off preference. She is a misandrist and hates men. - prejudice based off sexism. Hope that helps!