For 2000 years, knowledge was "Justified True Belief." Coined by Plato JTB is when:
- (a) Plato knows that [knowledge claim] is true if and only if
- (i) [knowledge claim] is true,
- (ii) Plato believes that [knowledge claim] is true, and
- (iii) Plato is justified in believing that [knowledge claim] is true.
In 1963, Edmund Gettier showed you need more than evidence to have knowledge with a similar case:
- (d) Aristotle will get the job, and Aristotle has 10 coins in his pocket.
- Plato believes (d) because the president of the company promised him that Aristotle would get the job and counted 10 coins in Aristotle's pocket
- (d) entails: (e) The man who will get the job has ten coins in his pocket.
However, Plato gets the job. Unknown to Plato, he has 10 coins in his pocket. Though (d) is false, (e) is true. And though Plato held a justified, true belief, he did not know that (e) was true through true logic.
That's why no one knows anything for sure. Sherlock Holmes gets lucky. Besides, true knowledge is devastating. Look at Paralyzed Horse or Spalko in Crystal Skull. Settle for Hitchhiker's Guide to the Galaxy or the Elder Scrolls and consume your "knowledge" in bits.
And when you think you know something, or worse, someone you're speaking with thinks they know something, rest assured they don't and neither do you. Just Google it, logic it, and call it what it is: an opinion.