Full Idea
Moore and Russell reacted strongly against the idea that the unity of the proposition depended on human acts of judgement. ...Russell decided that unless the unity is explained in terms of the proposition itself, there can be no objective truth.
Gist of Idea
Russell said the proposition must explain its own unity - or else objective truth is impossible
Source
report of Bertrand Russell (The Principles of Mathematics [1903], p.42) by Donald Davidson - Truth and Predication 5
Book Reference
Davidson,Donald: 'Truth and Predication' [Belknap Harvard 2005], p.100
A Reaction
Put like this, the Russellian view strikes me as false. Effectively he is saying that a unified proposition is the same as a fact. I take a proposition to be a brain event, best labelled by Frege as a 'thought'. Thoughts may not even have parts.