Is there any difference between active and passive feats?

Question

I've been wondering about feats: many of them, like Toughness, are "passive", so they are always working and PCs are always enjoying their benefits. Others, instead, like Power attack or Cleave, need to be declared before attempting to roll the dice. Is this difference actually present in Pathfinder, and if so, there are any special rules (sorry for such a generalization but I can't be more precise) that regulate them?

For example, my greatest doubt is about how many feats can I declare before attacking: can I, at the same time, use Power Attack, Vital Strike and then also Greater Cleave on the same enemy (and of course to all the other surrounding it)? Or I have to just choose between one of them, because just one "active" feat can be used per turn?

I've repeatedly searched the Core Rulebook but I haven't found anything about this. So is such a rule about feats just absent (and thus I can use as many feats as I want) or is it implied somewhere, or maybe I just missed it?

Answer 1

There is no such thing as "active feats" in the rules

In theory, you can declare to use as many feats as you like at the same time, provided they are compatible with each other.

A simple example of incompatible feats would be Rapid Shot and Power Attack. The former applies to ranged attacks, the latter to melee attacks, so you can't (normally) use both at the same time.

Other combinations of feats are far less obviously incompatible. Let's take a look at Power Attack, Vital Strike and Greater Cleave, since you mentioned it in your question. Power attack simply requires making a melee attack. Vital Strike and (Greater) Cleave are problematic however. The feat descriptions state

When you use the attack action, you can make one attack at your highest base attack bonus that deals additional damage.

and

As a standard action, you can make a single attack at your full base attack bonus against a foe within reach.

respectively. Vital Strike requires you to use the Attack action, which is a type of Standard action that involves making a melee attack. (Greater) Cleave is another Standard action type altogether, meaning you can't use both at the same time. Assuming you are using a melee weapon, you can combine either with Power Attack though.

Answer 2

Since it is not stated, there is no rule to cover it. There is no limit of feats, no passive/active feat distinction, etc. You don't see it because it's not there.

As many feats can come to bear on a given action as the rules otherwise allow - so yes, you can use Power Attack with Vital Strike or with Cleave/Great Cleave. You can't use Vital Strike and Cleave together however because Cleave is its own special standard action ("As a standard action, you can...") and Vital Strike modifies an attack action specifically ("When you use the attack action...") You'll find most of the limitations of combining feats have to do with the action economy or specifically saying "this doesn't stack with this other thing."

Answer 3

Another way of looking at this is to say that all of a character's feats are active all the time. Regardless of the benefit the feat grants you, its text always applies. The text for Great Cleave, which contains the rules for when you can use Great Cleave, always applies to your character ("As a standard action, you may...") even when you aren't actually using your standard action to cleave.

Likewise, Toughness (considered by some to be a "passive" feat) isn't an "activated" ability but its text is always "active" and applies the moment you take the feat ("You gain +3 hit points."). There is never a time when toughness does not apply to your character after this (you can't lose those 3 HP). It also continues to apply its other benefits as you increase in power ("If you have more than 3 Hit Dice, you gain +1 hit points whenever you gain a Hit Die (such as when you gain a level))."

Passive and active are metagame terms used by people to identify which feats grant you an activated ability (Cleave, Vital Strike, etc) and which feats grant your character a passive bonus (Toughness, Skill Focus, etc). There are no game-term rules that make this distinction -- it is simply something that arose from the metagame.