Look at the photo of a dollar below:

See where it says “Federal Reserve Note” and where it says “This note is legal tender…”?   Dollars are notes or debts, that is, obligations of the Federal Reserve.  When the Federal Reserve buys US Treasury Bonds from the open market  and pays for them with dollars (a process some refer to as “monetization” or “printing money”), it and the marketplace has simply exchanged one form of debt for another.  The supply in the hands of the market of one kind of debt (dollars) increased while another (Treasury Bonds) decreased.   Long before the Federal Reserve got involved to exchange dollars for Treasury Bonds – when the Treasury bonds were first created and sold to the public – that’s when the notional value (that is, the proceeds) of those Treasury Bonds was attached to goods and services.  Increases in government debt, as well as increases in private debt (net), are inflationary.  But not the monetization of the debt by the Federal Reserve.

At present, we have a situation where private debt is being reduced faster than government debt is being increased so that, in aggregate, total debts are declining – this is deflationary.

Technically, the total supply of debt can increase in an amount equal to the amount which society saves each year without inflation.  Conversely, total debt (including new equity shares) must increase by the amount of savings each year, or… we will have deflation.

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Read more on Federal Reserve, Debt at Wikinvest