How “principally” became a loophole
After the banking failures of the Depression, federal law restricted commercial banks from being closely tied to firms that underwrote or traded securities. Underwriting means helping companies sell stocks or bonds to investors. The law did not simply ban every connection: it allowed bank affiliates to conduct some securities business, so long as they were not engaged in it “principally.” The Federal Reserve had to decide what that elastic word meant in practice.
Bankers pressed the Fed to permit more activity. A strict reading would have kept securities work marginal; a looser one let an affiliate earn a larger share of its business from it while still claiming not to be “principally” a securities firm. The word stayed in the rule, but its practical boundary moved.
A boundary that changed the business
That distinction mattered because a bank could expand its reach without the law’s restriction disappearing on paper. As regulators allowed affiliates more room, banking groups could connect ordinary lending and deposits with a broader range of financial services. The permitted boundary was later widened further, helping set the stage for the growth of financial conglomerates.
This was not the sole cause of megabanks: mergers, other regulatory changes, and later legislation also mattered. But “principally” shows how a rule can be weakened through interpretation before lawmakers formally repeal it. A single undefined word gave regulators room to adjust the line—and gave banks a reason to keep asking where that line should be.
