Response to a Presuppositionalist

Presupper: “If we reject God, we cannot know anything.” 

To address this assertion, we need to keep in mind the distinction between these two claims:
1.) Those individuals that reject God know nothing.

or
2.) If God were to not exist, then we could not know anything.

(1.) represents the epistemic sphere, it concerns how people have knowledge.  It claims that if a person rejects God in their minds then they possess no knowledge whatsoever.  (2.) represents the ontic sphere, it concerns something out there in the world that’s independent of our mental life, God’s existence and his creation of the world which enables us to have knowledge.  The presupper's statement better mean (2.), because (1.) seems obviously false.  

But before saying more, we probably should try and define what we mean by “knowledge.”  Here’s a rough attempt that will work for our purposes: Knowledge = justified true belief.  So a person qualifies as possessing knowledge if they have a belief that is true, i.e., is actually the case, and if that belief is justified in some way.  Justification can be attained via a variety of means--either by evidence, or by testimony, or if the belief is a result of a reliable process (like sense perception), etc.  

With this short definition of knowledge in mind, we can ask: May a person that rejects God possess knowledge?  Sure they can.  Say that an atheist believes that it’s 2:00 AM.  So he meets the belief requirement.  Further, it’s true that it’s 2:00 AM.  So his belief meets the truth requirement.  Further, the clock telling him that it’s 2:00 AM is reliable.  So the belief meets the justified requirement.  So he possesses knowledge.  That it’s. He’s got knowledge. The atheist doesn’t need to first know that God sustains the world in existence or that God created the world in order to know it’s 2:00 AM, the atheist merely needs the elements above.  So it’s false that if we reject God that we cannot know anything, so (1.) is false.

Yet (2.) is true, because the atheist would fail to have knowledge if God did not create him and the clock in the first place.  We need to keep the ontic and epistemic concerns separate, or we’ll be confused.

So it’s true that the atheist would know nothing if God did not exist, but this is a point about the reality of the case, not about the personal knowledge of the atheist.  Here’s the distinction at work: (a) The atheist does not need to know that God exists in order to know what time it is, but (b)  it is the case that he knows what time it is because God exists.