I’m going to be busy this week, so I don’t know if I have the time to constantly engage on this topic. (Also, arguing simultaneously with 3 or 4 aggressive skeptics, as happened last weekend, is emotionally and intellectually tiring. It’s like a chess match between three computers against one computer. 
)
The type of sensus divinitatis (SD) most recently proposed in philosophy is the one that Plantinga talks about. I’m not an expert on it. I don’t know if Plantinga’s argument works, and I’m arguing in favor it more for fun rather than because my position as a Christian rests on this argument. It would be more interesting and fun if the regularly aggressive posters here would consider the argument seriously and look for ways to patch or modify it if it doesn’t satisfy them, rather than just dismissing it as gibberish or garbage. This argument is not designed to rationally oblige you to become a theist, so don’t be afraid!
To start with, I found this essay on Plantinga with a passage which concisely gives an idea of what Plantinga’s SD is:
The sensus divinitatis is rather a capacity, like memory or perception, that all humans have, that allows us to form beliefs about God. It is by interacting with the world that we actually come to have beliefs about God—just like we must interact with the physical world to perceive it or make memories about it. The sensus divinitatis “works in response to the sorts of conditions or stimuli that trigger the working of this sense of divinity.” When we see a beautifully verdant meadow or an immensely rugged and majestic mountain or the hustle and bustle of people in a city, beliefs about God simply arise within us. Plantinga argues that rather than providing the premises for an argument, our circumstances simply occasion the rise of such beliefs within us. It is not because the Australian outback is menacing and dark that God exists. Plantinga argues that this notion would be logically fallacious. Rather, our perception of the outback causes such a belief to come forth. We develop our knowledge of other minds in a similar way. We are not born with the knowledge that other people have minds, but in our interactions with other people, we simply come to believe, consciously or unconsciously, that other people have minds. The sensus divinitatis works in a similar way.
What’s very important to note here is: Plantinga isn’t arguing that God exists based on the SD. Nope. Rather, he’s arguing that if God exists, then our belief in God is warranted (which is a more technical term for “justified”), even if we don’t have other proofs of God’s existence. So if your response to this argument is “But you haven’t proven that God exists! That’s not knowledge!” Well, duh. That’s not the point of the SD.
The original hypothetical experiment regarding sight that Faizal brought up is thus not really relevant to the issue of SD, as originally argued by Plantinga. I don’t think it’s possible to demonstrate SD to someone who doesn’t have it. God is not like light, which we can control. SD is not exactly the same as one of our five senses. Demonstrating that SD exists would essentially be demonstrating that God exists, and Plantinga doesn’t believe in natural theology (I remember reading).
My argument for “demonstrating” SD
However, Faizal’s hypothetical experiment is responding to my half-baked attempt (not Plantinga’s) to demonstrate how believing that one has an SD could be justified even from the point of view of those who don’t have it. I’m not sure if my argument works. It is basically a variety of an argument for the veridical nature of religious experience - i.e., that I am warranted to treat religious experiences as giving me true knowledge of God. As you’ll see, it might not even be an argument to “demonstrate” that SD exists, only to illustrate the gulf that exists between theists and non-theists. So let me give it a try.
First, I think that it’s clear the experiment brought up misses the point of my argument. The experiment only proves that “sighted” people have some capability to distinguish between 2 and 3 fingers. They are “perceptively superior” to the blind person in some way. It does not prove that the experience of seeing light exists, nor even that light itself exists. And by the latter I mean light as experienced by sighted people, not light as some phenomena that you can duly record using a detector via the photoelectric effect, for example.
From the blind person’s point of view, it could be the case that another mechanism or experience than sight is responsible for how the “sighted” person perceives the fingers, for example, a heightened form of perception more similar to touch or smell or instinct that activates whenever these alleged experiences of “sight” happen. The “sighted” person is merely misinterpreting her experience as “seeing light”. Thus, the blind person seems to have no obligation to believe that light specifically exists. The only thing the “sighted” person could say to him is, “If only you had my eyes, then you would be convinced that light exists. It’s light that causes me to be able to see your fingers. It’s a really different experience than touching or smelling!”
Now let us apply this to the case of SD. Let’s pretend that I have SD and Faizal doesn’t. Faizal observes that whenever I pray or see a waterfall, I claim that I perceive God. He puts electrodes on my brain to track that, and yes, a certain part of my brain lights up every time I do one of these activities. (The point is that my reaction is pretty reliable.) However, Faizal does not react in the same way whenever he does the same activities as I do. Like the blind person in the experiment, he cannot deny that there is something in the way my mind or brain works that causes it to experience something that I interpret as “perception of God”. But instead of God, Faizal interprets it as nothing more than a random chemical reaction happening in my brain that happened to latch on purely by coincidence in the evolutionary process. Perhaps it is merely a “heightened perception of food” or “heightened perception of safety” instead of “perception of God”. Food and safety are things that Faizal knows exists and has experienced. But not God.
Towards this charge, I cannot prove that my perception is real to Faizal, because I cannot share my first-person experience of it to him. All I can say to him is, “If only you had my perception and my experience of seeing this waterfall, then you would be instantly convinced that God exists.” Faizal then responds, “Too bad then that I don’t have that experience.”
We leave in peace, unmoved by the other. Neither of us are behaving irrationally. It’s just that one has access to an experience that the other does not. Faizal is not obligated to believe in God. He is perfectly justified to suspend belief about what it is that I’m experiencing. He is, however, obligated to believe that (assuming I am not lying) there is something about my mind and/or brain that makes me react differently than he does, and that I claim that it justifies my belief in God.
Does it obligate him to believe that I am actually justified, as opposed to merely claiming to be justified? This is the part that I’m not sure about. I personally tend to be generous about defining justification, so I would say yes.
