Well, its form could conceivably be different. &quot;Generally accepted medium of exchange&quot; is one definition. But in the case of national fiat, it&#x27;s also the unit of account and store of value. More broadly, it&#x27;s an accounting device for intertemporal coordination of savings-investment decisions. Private currencies would be especially apt in the latter case.<p>Certainly some systemic cooperation would be in order to maintain reflux, but it&#x27;s more reliable than deposit insurance when people&#x27;s equity is at stake.<p>Social safety nets can be ensured from a myriad of techniques.