It's a great privilege to be able to watch Professor Scott's lecture after the event via the web. Of course I know of his work in logic, etc., and the talk was rich with examples and observations.

With regard to social constructivism as a philosophy of mathematics I didn't feel very strong arguments or critiques were given that haven't already been countered or anticipated by those of us working in the field. See for example my paper 'Is mathematics discovered or invented?' <http://www.people.ex.ac.uk/PErnest/po...> that treats an issue explicitly discussed in the Q & A session at the end. I had a sense of Professor Scott's beliefs, but I'm not so sure that his arguments would sway a neutral listener.

I found the critique of Michael R. Matthews (Social Constructivism and Mathematics Education: Some Comments) given at <http://www.ed.uiuc.edu/EPS/PES-yearbo...> had more force, although needless to say I remain a committed social constructivist.

Overall, I felt this was more of a popular mathematical lecture than a philosophical one, although philosophical issues were raised; and welcome one at that.