I was driving along the highway, when I happened to notice the scenery. It was evening twilight, and the observation was made that at a certain point, one cannot really tell whether it is morning or evening twilight.
Here is a picture of (supposedly) morning twilight, from the internet.
Ok.. Now here is a picture of (supposed) evening twilight, from the internet.
Both pictures are pretty much the same. If I were to ask you whether you could tell which is which without giving you any other information and only those pictures, you wouldn't be able to do it with any **degree of confidence**.
How does this mundane example relate to presuppositional apologetics and also in discussions about ethics?
We know that one cannot understand truth (any kind, moral or ultimate etc...), especially truth about God's existence, by simply going off one's senses. In the "How to Answer a Fool" apologetics DVD, Sye Ten Bruggencate laser focuses in on this assertion when it is made by atheists.
"From my observations from the natural world, I conclude that God does not exist!" (typical atheist response).
How does this relate to the evening and morning twilight? Simply just looking at the morning and evening twilight, without any additional information.... or a standard being given (revealed) to you, you cannot know for certainty whether or not what you are observing with your eyes (using your senses) is the morning or evening. In this mundane example, it is easy to see how your senses cannot ever tell you this information, on something as simple as determining whether you are seeing a morning or evening twilight picture.
You ***know*** that it is an evening twilight because you have a watch that tells you the time (or at least, you have been informed on what time the pictures were taken). You have clear "revelation" (the information from the watch) that informs you and makes *sense* of what your senses are giving you. Based on what you know (from your watch), then that knowledge then enables you to interpret what your sensing (seeing).
From those two pictures above, there is no other way for you to know whether the twilight is morning or evening without that information, or standard.
The same goes for ethical truths. We cannot simply "sense" or feel that something is wrong or right. While this deals with the motivational aspect of ethics, this is never the foundational reason why a particular action is wrong. It is wrong because of a normative standard. This normative standard has to be revealed to you (which it has been, through nature and ultimately through Scripture, Rom 1) so that you can know based off the normative standard.
If we cannot even determine something as simple as the truth of which twilight is which from our own senses (visual perception in this case), how can atheists possibly make the bold assertion that through their observations about the natural world (senses) that they can **for certainty** determine and **know** that there is no God?
You can't. You can **never** determine the truth of a knowledge claim based on your senses.
It's crazy, but we know why they make this claim: because of the total depravity that has infected their mind and their heart.
I think that this twilight example is a very easy and yet very effective way of helping atheists to see how their senses cannot determine truth at all and cannot be used to make knowledge claims, and that the truth has to be revealed to them, and it has been.. again, according to Romans 1.