Validity & Assumptions
The shape of a good inference
Valid, Sound, and Hidden
Logicians separate two things we often blur. An argument is valid when its conclusion truly follows from its premises, the shape is correct. It's sound only when it's valid and the premises are true. A valid argument built on a false start still leads you astray. Watch, too, for hidden premises: the unstated assumptions quietly doing the real work.
“The least initial deviation from the truth is multiplied later a thousandfold.”
Where this sits in the course
“Validity & Assumptions” is lesson 2 of 2 in Reason & Its Traps, a course about before arguing, learn the shape of good and bad reasoning.. The lessons are sequenced rather than a menu, so this one assumes what came before it.
Reason & Its Traps is itself one of 18 courses in thinkr. The set opens with what philosophy is, moves through the Stoics and the Eastern traditions, then into what can be known, what exists, how to act and how power works — closing on practical reasoning you can use in an argument this week.
More from Aristotle
“Knowing yourself is the beginning of all wisdom.”
“We are what we repeatedly do. Excellence, then, is not an act, but a habit.”
“Happiness depends upon ourselves.”
In the app this lesson is followed by 3 exercises that check whether the idea actually landed — and every answer, right or wrong, is explained rather than scored. That is the part a written page cannot reproduce.