How can you tell a fact from an opinion?

A fact is information supported by proven data and evidence. Opinion is the personal view held by an individual on any given topic. However it is not always easy to tell one from the other, since there is no fact that does not have someone who disputes it and provides something purporting to be "data and evidence" to support it. A number of things which were thought to be facts in the past have since been disputed and are no longer believed. The best we can say is that information is factual if, given our present beliefs and understanding, the overwhelming majority of people and especially those who purport to be experts in the field accept as their opinion that it is factual. Opinion is therefore an individual thing, but the idea of fact depends on social consensus of opinion.