How do I identify Neutral Vs.Ground?

I have an older house so the wiring is cloth wrapped and NOT color coded. I have 4 cloth wrapped wires in a ceiling junction box. 2 of the wires I have determined as hot/live with a circuit tester. The remaining 2 are, i believe, my neutral and ground. However, I am not sure how to determine which is which and they attached to different location on a new light fixture I am installing.