According to the fact/value distinction, factual statements about the world are different from value statements about what is good/bad, moral/immoral, just/unjust, etc. And the latter cannot be deduced in any straightforward way from the former.
Now, recently, Sam Harris has argued against the fact/value distinction. For Harris, values are simply one kind of facts: they are facts about the well-being of sentient creatures.
Since it is often thought that science deals with facts and must remain silent about value questions, Harris rejects the fact/value distinction in order to argue that science can answer moral question. His overall argument seems to go something like this:
- Moral questions are questions about the well-being of sentient creatures.
- Science can answer questions about the well-being of sentient creatures.
- (Therefore) Science can answer moral questions.