I'm going to reveal science's dirty little secret.
I rest assured that this will turn the scientific community on its ear. Someone put Stockholm on speed-dial.
If it's raining then the roof is wet.
The roof is wet.
Therefore it's raining.
Well, the problem here is that the third statment won't be "therefore it's raining." It'll be a lot closer to the following:
If it's raining, then the roof will be wet.
The roof is wet.
All right, now we're getting somewhere.
Is there anything else could have made the roof wet?
Oh, there is? Okay. What else would we see if it was raining?
Maybe water falling from the sky? Somebody check if there's water falling from the sky.
There's water falling from the sky.
All right, now we're getting somewhere.
Repeat as necessary.