A Simple Point of Logic Journalists Ought to be Aware Of

One often encounters sentences like this one:

There are many arenas in which all ideas are not considered equal.

This example is from a recent piece in Vox. I could give further recent examples, but one is enough. To simplify, consider just the core thought:

All ideas are not considered equal.

Unfortunately it is not entirely clear what the core thought is. For the sentence is ambiguous as between 

1) No ideas are considered equal

and

2) Some ideas are not considered equal.

The thoughts (propositions) expressed are distinct since the first can be false while the second is true. Although it is fairly clear that the author intended (2), a good writer avoids ambiguous constructions unless for some reason he intends them. So don't write sentences of the form

3) All Fs are not Gs 

if you intend say something of the form

4) Some Fs are not Gs.

Write instead sentences of the form

5) Not all Fs are Gs

which, by simple quantifier negation, is equivalent to (4). 

Class dismissed.