Originally Posted by PF SRDThe first quote gives the general rules for counterspelling. There is, oddly, no requirement that you be a be able to see and/or hear the caster. In fact, as written in that section, I could choose to counterspell the king's personal healer, even if I'm half a world away.Originally Posted by PF SRD
The Spellcraft skill, however, does give a bit more detail. It lays out that you have to see the spell being cast, which rules out the half-a-world-away counterspell. So what's it mean? Well, it doesn't say you have to see the somatic components or the material components or the focus. It just says you have to be able to see the caster as he/she/it casts the spell. Do that and you get a Spellcraft check with a DC of 15 plus the spell level. If you're successful at that check, you know what spell is being cast. If you had taken a ready action to counter, you could then attempt to counter the caster - despite his having used Still and Silent and not needing any components.
At least, that's how I read it.
SpoilerYou could opt to explain this in your game by having the Spellcraft check read the ambient magical energy around the caster rather than the actual act of casting. A successful check allows you to read the "aura" building around the caster before the spell's energy coalesces into the spell effect. In this way, it's not the gestures and words and pieces of bat poop that matter when identifying the spell, and it gives a nice reason as to why a Silent Still fireball cast by a wizard with Eschew Materials can still be identified.