One relevant fact that is missing from most analyses of inflation and deflation is the fact that for spending purposes currency and credit are fungible.
No, it is not missing.
http://en.wikipedia.org/wiki/Money_supply - People spend lots of time trying to figure out exactly how much money there is because of credit.
The US experienced severe periodic inflation and deflation on the gold standard because while the gold supply was relatively stable, the credit supply was alternatively expanded and contacted by the banking system.
And this is a problem with the government-given gift of central banks, not a locked or unlocked supply of money.
Depressions are normally associated with depression because they are always preceded by a collapse of the credit markets. The question that we should be asking is, "Why does the credit supply keep getting so large compared to the currency supply, and why is it always allocated in such a way that it periodically collapses and causes a depression?"
Chicken and egg solved? I don't think so. The credit markets collapse because credit is overextended, overproduction and overconsumption are rewarded, and banks always win. The "banks always win" part is by far the most important, because no matter what happens they will fuck society in the ass without lube.
Saying that we need inflation to avoid a depression is like saying we need to keep drinking to avoid a hangover. The right solution is to stop getting drunk on cheap credit in the first place so that we don't need to worry about currency appreciation caused by increased productivity.
Saying that we need deflation to avoid prosperity...
http://hayekcenter.org/?p=5401FA Hayek: “I agree with Milton Friedman that once the Crash had occurred, the Federal Reserve System pursued a silly deflationary policy. I am not only against inflation but I am also against deflation. So, once again, a badly programmed monetary policy prolonged the depression.”
And increased productivity does not cause currency appreciation, it causes lower prices. There is a difference. There isn't more demand for the currency when prices go down; that would be silly.
I am not a keynesian, and I have never said we need inflation to avoid a depression, so please don't put words in my mouth or create a strawman. But then again, you may have not been responding to me since you just went off on a typical bitcoin diatribe after you realized you lost the argument. So, if that's the case, carry on.