Does the Aptitude enhancement work with Shadow Blade

[tedcahill2]

If I have the Shadow Blade feat and a great sword with the aptitude enhancement can I add my dex bonus to my great sword damage?

[Eldariel]

...depends on how liberal the DM's reading of the Aptitude enhancement is. Strict RAW? Probably.

[Red Fel]

If I have the Shadow Blade feat and a great sword with the aptitude enhancement can I add my dex bonus to my great sword damage?

Well, let's consider each in turn.

First, the Aptitude weapon enhancement. According to that enhancement, a wielder who has feats specific to a type of weapon, like Weapon Focus or Weapon Specialization, can apply those feats to an Aptitude weapon. These are feats that call out a specific weapon, such as longsword or crossbow or unarmed strike.

Next, the Shadow Blade feat. According to that feat, while in a Shadow Blade stance and using one of Shadow Blade's discipline weapons, you can add Dex to damage.

There's a strict reading, two less strict readings, and a broad reading.
Strict reading: Aptitude deals with weapon-specific feats. The ones in the example require you to designate a specific weapon, such as Weapon Focus (longsword). Shadow Blade is not that type of feat, and therefore Aptitude would not apply.
Less strict reading: Aptitude deals with feats that call out a particular weapon. Shadow Blade doesn't call out a particular weapon, but rather applies to a group of weapons, and therefore Aptitude would not apply.
Other less strict reading: Aptitude functions as a word-substitution. You take any instances of (weapon name) in a feat, and replace it with the Aptitude weapon. However, because Shadow Blade doesn't name any weapons, you can't substitute your Aptitude weapon for it, and therefore Aptitude would not apply.
Broad reading: Aptitude just lets you apply weapon-based feats to your current weapon. Shadow Blade is a weapon-based feat, kinda, so it should apply.
In summary, Aptitude probably doesn't work with Shadow Blade. However, talk it out with your DM; you might get a more lenient reading.

[Tytalus]

The Aptitude enchantment states: "A wielder who has feats that affect the use of a particular type of weapon (...) can apply the benefits of those feats to any weapon that has the aptitude quality."

The only question is, does Shadow Blade "affect the use of a particular type of weapon"?

And the answer is "yes". Shadow Blade even affects the use of multiple particular types of weapons, namely the Shadow Hand weapons listed elsewhere in the book.