Alignment

In Fate/stay night, all of the Servants' alignments can be viewed on their respective status screens. The first part indicates the principles they consider important, and the second part indicates personality.
Below is a complete list of alignments featured in the game, for comparison purposes.

SaberLawful Good
LancerLawful Neutral
ArcherTrue Neutral
RiderChaotic Good
CasterNeutral Evil
BerserkerChaotic Insane
AssassinLawful Evil
KojirouNeutral Evil
GilgameshChaotic Good
Saber AlterLawful Evil


While a difference in personality generally won't be too much of a problem, a difference in principles will inevitably lead to friction.
Saber and Gil would be a good example of that.

Fate/side material: Fate Encyclopedia