Full Idea
Russell's account of names and definite descriptions was concerned to preserve the law of excluded middle, according to which every sentence is either true or false (but it is not obvious that the law ought to be preserved).
Gist of Idea
Russell's theories aim to preserve excluded middle (saying all sentences are T or F)
Source
comment on Bertrand Russell (On Denoting [1905]) by Sarah Sawyer - Empty Names 3
Book Reference
'Routledge Companion to Phil of Language', ed/tr. Russell/Graff Faria [Routledge 2015], p.156
A Reaction
That is the strongest form of excluded middle, but things work better if every sentence is either 'true' or 'not true', leaving it open whether 'not true' actually means 'false'.