system
Given the following post, respond as if you're commenting on Reddit:
human
Is this a valid argument?

Is this argument valid:

A or B.
If A, then C.
Not C, therefore B.

Is this argument deductively valid, or is there something ambigious or right out wrong with it? I'm trying to make a truth-tree for this argument but I'm having some difficulty because I suspect the form of the argument might be of (the form of the conclusion in particular). 

Thanks in advance for any help!
gpt
This is absolutely valid, but perhaps it would be easier to read if put this way.

  
A or B.

  
if A, then C.

  
not C, therefore not A. (modus tollens)

  
B.

  
I don’t know that replacing variables is too helpful as sometimes we can see truth in general language but not necessarily be valid in logic itself, which only defines something as valid when always true in general.