Thanks mods for the title fix.

I can't find a copy of the letter this is in response to which would provide more context. I believe it was an invitation of some sort.

Bertrand Russel was a prominent logician and philosopher, more or less invented types to solve a problem he was having with set theory.

https://en.wikipedia.org/wiki/Bertrand_Russell

Sir Oswald Mosley founded the British Union of Fascists.

https://en.wikipedia.org/wiki/Oswald_Mosley

> more or less invented types to solve a problem he was having with set theory.

For people who haven't encountered it yet, this problem is the famous "Russell's Paradox"[1], which can be stated as

Consider the set R, consisting of all sets S such that S is not an element of S.

Ie in set builder notation

R = {S : S ∉ S}

and then the paradox comes from the followup question. Is R an element of R? Because of course if it is in R, then it is an element of itself so it should not be. And if it's not in R, then it is not an element of itself, so it should be. This is a logical paradox along the same lines as the famous "The barber in this town shaves all men who do not shave themselves. Does he shave himself?"

In modern axiomatic set theory, Russell's paradox is avoided these days by the "axiom of regularity"[2] which prevents a set builder like "the set of all sets who are not members of themselves", so what I wrote above would not be accepted as a valid set builder for this reason by most people.

Russell proposed instead Type theory which got revived when computer science got going.

[1] https://en.wikipedia.org/wiki/Russell%27s_paradox

[2] https://en.wikipedia.org/wiki/Axiom_of_regularity

Bertrand Russel also was - and hopefully still is - a public intellectual, like Einstein or Chomsky (for better or worse), whose opinions on many areas of life reached ordinary people. His values were ahead of his time.

This is a wonderful interview with him that gives a great sense of what he was all about:

• A Conversation with Bertrand Russell (1952) https://youtu.be/xL_sMXfzzyA

They had a long history of correspondence. The preceding letter is archived and you can probably get a copy. (https://bracers.mcmaster.ca/79128)

> Jan 6/1962 Re nuclear disarmament and world government. BR is not inclined to agree or disagree with Mosley's views, but he does think that Mosley is "rather optimistic" in his expectations. BR provides criticism of his main two objections. (A polite letter.)

> Jan 11/1962 Mosley wants to lunch privately with BR about their differences.

These are basically all the letters exchanged with Mosley:

https://bracers.mcmaster.ca/bracers-basic-search?search_api_...

For general context, this was addressed to post-ww2 Mosley, in the 60s, who argued a unique form of holocaust denialism at the time. He didn’t take the position that the holocaust didn’t happen, he took the position that it was justified.

Mr Mosley also had a pretty well known son lol.