The relationship between X and Y as evidence and outcome isn't just about whether we can personally think of a connection, it's about whether there is a logical, empirical, or probabilistic connection that can be established. Let's think about this through three different lenses: Deductive reasoning, Inductive reasoning, and Abductive reasoning.
- Deductive reasoning: In this form of reasoning, if the premises are true, the conclusion must be true. For instance, if we have the premises
- All men are mortal.
- Socrates is a man.
We can deduce the conclusion:
Here, the premises are evidence for the conclusion. If you can't find a logical structure that connects X and Y in this way, then X is not deductive evidence for Y.
Inductive reasoning: This is where we generalize from specific observations to broader truths. For instance, if we observe that the sun has risen every day of our lives, we might inductively infer that the sun will rise tomorrow. If X is an observation that fits into a pattern that leads us to anticipate Y, then X is inductive evidence for Y.
Abductive reasoning: This is often referred to as "inference to the best explanation." We use this kind of reasoning when we have some data and we're trying to figure out the best explanation for that data. For instance, if you wake up and see snow on the ground (X), you might reasonably infer that it snowed last night (Y). Here, X is evidence for Y because Y is the best explanation we have for X.
Now, let's consider your example about seeing a plane and someone in your house getting murdered. Generally, we would say that these things are unrelated because there's no commonly accepted logical, empirical, or probabilistic structure that links them. It's not about you personally being unable to think of a connection; it's that there's no widely recognized reason to think there is a connection.
However, in some very specific contexts, seeing a plane could be evidence of a murder in your house. For example, if there was a known serial killer who always flew a distinctive plane over the houses where he committed murders, then seeing that plane might indeed be evidence of a murder in your house.
So, when you're asking whether X is evidence for Y, you're essentially asking whether there's a logical, empirical, or probabilistic structure that connects X and Y. If there isn't, then X is not evidence for Y.