Full Idea
The law of excluded middle may be stated in the form: If p is denied, not-p must be asserted; this form is too psychological to be ultimate, but the point is that it is significant and not a mere tautology.
Gist of Idea
Excluded middle can be stated psychologically, as denial of p implies assertion of not-p
Source
Bertrand Russell (Meinong on Complexes and Assumptions [1904], p.41)
Book Reference
Russell,Bertrand: 'Essays in Analysis', ed/tr. Lackey,Douglas [George Braziller 1973], p.41
A Reaction
'Psychology' is, of course, taboo, post-Frege, though I think it is interesting. Stated in this form the law looks more false than usual. I can be quite clear than p is unacceptable, but unclear about its contrary.