[datashow]

"First" does not equal to "cause" either.

[luckylion]

Second rules out cause though. If you have A=>B and B=>A as possibilities, and you can rule one of them out with a very simple question, that's a good way to start.

If computers came after electricity, they didn't cause electricity. That says nothing about the possibility of electricity causing computers, but it brings us forward nonetheless.

[jjk166]

First doesn't necessarily cause second, but second almost certainly doesn't cause first.