Would a feycraft whip be redundant?

[Masakan]

I just wanted to ask this for clarity, adding the feycraft template to a whip or a rapier, does not allow you to use it without weapon finesse does it?

[Chemus]

...are treated as one size category smaller than normal for the purpose of dealing damage. For example, a feycraft short sword sized for a human deals 1d4 points of damage rather than 1d6. If the weapon would normally be considered one-handed, it can be treated as a light weapon for the purpose of the Weapon Finesse feat, but not for any other purpose. If the weapon would normally be considered light, the wielder can apply his Dexterity modifier instead of his Strength modifier to attack rolls made with it, as if he had the Weapon Finesse feat.

You can use the Weapon Finesse feat to apply your Dexterity modifier instead of your Strength modifier to attack rolls with a whip [or rapier] sized for you, even though it isn’t a light weapon for you.

Yes, RAW they overlap rather than stack. Neither whip nor rapier is considered a light weapon for the purpose of weapon finesse; they both merely permit the use of the feat. It's pretty reasonable to have the properties stack as a house-rule to have them stack, though.

[ketaro]

Well if you're saying per RAW, isn't "considered light" entirely different from very plainly have just said "if it already is a light weapon"?

So they do stack, not overlap, per RAW, yes?

[Chemus]

I should have said that the rules for each don't interact at all; rapier and whip are medium weapons that, when properly sized for a creature, just happen to be eligible for the weapon finesse feat. Feycraft weapons are considered to be one size lighter than they would otherwise, and if already considered light (being light qualifies as considered light, but considered light doesn't qualify as is light, except for whatever it's considered light for (Weap. Fin.)) they may be finessed without the feat. Neither affects the other.

I used 'overlap' as shorthand. And they do overlap.