"The basic cause is mental"

The neglect of relevant distinctions, when these are important for clear thinking or adequate statement, is ambiguity.

R.W. Sellars, The Essentials of Logic (The Riverside Press, Cambridge, Massachusetts, 1917)

And what causes ambiguity? "The basic cause is mental" whatever that means. 

Only he who is willing o take the trouble to distinguish things and ideas which are ordinarily grouped roughly together, can escape the pitfall of ambiguity.

 Don't say I didn't warn you!

(How sad is it that I already have a tag, "logic?")