Is it "biased towards" or "biased against"?

I've come across both phrases for quite some time and I can't seem to distinguish the difference between both of them.

Suzy is biased towards Thomas.

Suzy is biased against Thomas.

In both cases, it is clear that Suzy holds something against Thomas; but what is the difference between "biased towards" and "biased against"? Is it the degree of bias or is it that both are acceptable?

Suzy is biased against Thomas can mean only that she has a prejudice against him. Suzy is biased towards Thomas is ambiguous. It can mean either that her attitude towards him is biased one way or another or that she is biased in favour of him. For that reason, it is perhaps best avoided.

I don’t think “biased towards” is ambiguous... Understand the meaning of bias, just google the meaning, read both noun and verb (and carefully read google’s examples under noun and verb). From a metaphorical perspective, bias is a teeter-totter that has a push (which is against) and pull (which is toward). Simple example: I’m biased towards the color blue (I like the color blue); I’m biased against the color red (I dislike the color red).

"Biased towards" means that there is bias, whether positive or negative, when considering a topic. This is typically used when having a positive bias towards a topic. "Biased against" is always when there is a negative bias towards a topic. ie. There is a negative connotation attached to the word "against" due to its other uses.