Full Idea
Some thinkers say that when some people are unable to resist pleasures then what they have is not knowledge but only opinion.
Gist of Idea
Some people explain akrasia by saying only opinion is present, not knowledge
Source
Aristotle (Nicomachean Ethics [c.334 BCE], 1145b33)
Book Reference
Aristotle: 'Ethics (Nicomachean)', ed/tr. ThomsonJ A K/TredennickH [Penguin 1976], p.228
A Reaction
You would have thought that people take their own opinions for knowledge, but Aristotle seems to refer to weakly held beliefs. Aristotle allows that this might excuse mild misbehaviour, but not true vice.