Ti values external rules over internal rules. This includes those of science, math, government, religion, society, club/association/similar organization, company, etc. You'll hear things like, "There are rules. Someone can't decide that those rules don't apply to them just because that person doesn't feel like they should."
Fi values internal rules over external rules. They concern themselves with personal likes and dislikes, an individual's own self-decided moral values, etc. You'll hear things like, "It's your responsibility to do what you think is right, even if it's against the rules."
(Not that Ti types are law abiding and Fi types aren't. Obviously.)