Welcome to the fourth of our TIME 100 special issues profiling the hundred most influential people of the century. We began a year ago by picking 20 leaders and revolutionaries, followed by artists and entertainers, then business titans. Now comes our convocation of the greatest minds: this century's 20 most influential scientists, thinkers and inventors.
Among the most interesting debates we had, especially with our outside experts, were those concerning the relative influence of thinkers vs. tinkerers--those who work mainly inside their own mind vs. those who turn their mind to practical things. In some centuries the tinkerers are more...