The 1914 Clayton Act prohibited any acquisition whose effect may be to “substantially” lessen competition. International Shoe defined § 7's word “substantially” by saying that an acquisition's effect is “substantial” only if it “will injuriously affect the public.” This paper...

Mergers that substantially lessen competition are illegal, but mergers that lower costs enough benefit society, so a merger of competing firms may be good for society if it generates enough efficiencies. Nonetheless, it is widely believed that the Supreme Court has not yet accepted an...