Brace yourselves for an analogy.
Imagine, if you will, a world where we don't know anything about beavers or beaver dams. We're exploring a new continent.
Then, one day, our exploration group comes across a strange structure in occasional ponds and streams (you and I would identify it as a beaver dam). This phenomenon is now observed. We have no idea how they form, or why.
We stand around, pondering these strange structures, when someone in the back pipes up.
There's probably a small mammal with an oval flat tail, and big buck teeth, that gnaws down trees and builds these structures. Since this structure exists, that demonstrates this creature exists.You an I would know this person is technically correct, but he/she would be right for the wrong reasons. This person just plucked it out of thin air, and just happened to be correct, without appealing to any evidence, observation or data.
What if he/she said this instead?
There's probably a rainbow dragon with fourteen tongues, that ninja-chops down trees and build these structures. Since this structure exists, that demonstrates this creature exists.Now he/she would be wrong, but notice that all we did was swap one assertion with another... and yet the structure of the argument is the same. Setting aside the fact that dragons are less common than mammals, and that'd drastically reduce the probability of the assertion being true, it should be obvious what the problem is.
If we take it another step further, and swap the beaver with "God", and the beaver dam with "Earth", we get:
There's probably a God that makes planets. Since Earth exists, that demonstrates God exists.It's technically true that Earth is evidence for planet-causing things, but one can assert an endless list of planet-causing things, and Earth's existence would equally support them all (i.e. not much).
We do know that beavers exists, and they create beaver dams... but how do we know this?
- We observed that these dams exist.
- We observed that beavers exist.
- We observed a causal link between beavers and the damns, as we observed beavers making them.
Our knowledge has then confirmed Phenomenon A, Phenomenon B, and the Causal Link between A and B.
When it comes to Earth, and it being created by a god, we're still waiting on #2 and #3.