Do Blur and Invisibility stack?

[Mudguard]

After an initial attack on the spell-caster, blur will still penalize his opponents with a -2 to hit. If the spell-caster subsequently casts invisibility on himself, and assuming his opponents aren't high enough to see invisible creatures, his opponents have a -4 to hit. Do these penalties stack? If it's the visual effect of blur which penalizes opponents, and that effect is not present, is the penalty still there?

[TRP]

It would only stack for creatures able to detect invisible beings. Otherwise, it's just the invisibility.

[grodog]

Unless of course the blur renders invisibility less effective

[TRP]

Unless of course the blur renders invisibility less effective

That's a good point. The target would be invisible, but there could be a detectable, blurred outline since the air around the target is unaffected by invisibility. Invisibility 10' radius could take care of that, but the personal version ...

I like the way you think!