The 3 Sources of Returns for Warren Buffett's Original Partnership

I was recently reading through Buffett's Partnership Letters (which can be found here) and stumbled upon something that he mentioned numerous times that I've never seen mentioned anywhere else before. Buffett classified his investments into three categories that he believed would have various correlations with the market. He believed that by splitting his capital up into general issues, work-outs, and control situations, he could better protect his downside in order to out-perform the Dow Jones long term.