本文闡述三個觀念，儘管這些觀念非常基本，在中國貨幣史的研究中卻極為欠缺：（一）貨幣的主要作用，是提供商品交易所需的「流動性」，以減低交易費用。（二）價格決定於貨幣總量與商品總量的比例。貨幣過多造成通貨膨脹，過少則造成通貨緊縮；前者意味著流動性過剩，後者則意味著流動性不足。（三）經濟體中，通貨數量的膨脹與緊縮有一傳遞的過程，故對價格的影響有先後與程度之別。上述三點的進一步涵義是：（一）歷史上布帛、穀物等「實物貨幣」與五銖、通寶等「正式通貨」的差異，正在於其所內含的流動性的不同。（二）貨幣數量的變動，將對經濟體的運作帶來流動性衝擊。（三）流動性的劇烈變化不僅造成價格起伏、市場動盪，且將惡化貧富之差距，加深社會、政治危機。晚近有的學者認為貨幣的退藏無損於「貨幣經濟」；有的則專注於各朝代的貨幣發行，卻無視貨幣數量變動對社會經濟的破壞作用；還有的從「手交貨幣」的方式論述貨幣「非對稱性」的存在，主張各地域存在不同的通貨偏好（所謂「自律性」），因此貨幣的多元紛歧不會造成市場的紛擾。依照作者的論點，這些說法忽略了流動性、交易費用與價格傳遞作用等方面的考量，在分析上是有所不足的。

This paper provides three notions: (1) Currency's main role is to provide "liquidity" in market in order to reduce transaction costs. (2) Too much money causes inflation and too little money causes deflation; the former means liquidity surplus, the later means liquidity shortage. (3) The expansion or contraction of currency quantity is a transmitting process, so that their impacts on market prices vary with time. These three points have further meanings: (1) Commodity money and official-issued metal currency are different because of their distinct modes of market liquidity. (2)Changes in the quantity of money bring liquidity shocks to economies and cause redistribution of wealth by price-transmission-mechanism. (3)Therefore, dramatic changes of liquidity will cause market turmoil and widen the gap between rich and poor, and deepen social and political crisis.In addition, this study points out flaws in some researches that ignore considerations of liquidity, transaction costs and the price-transmissionmechanism in their analyses.