All 3 of these “separate” goals (more purchasing power, more facilitation of transaction, more security) are essentially about the same thing. As Mises wrote, there is one and only one function of money: to facilitate exchange by serving as a medium of exchange. All other “secondary” functions that economists perorate about are really special instances of the one function.
Mises, TMC: “all of [the “secondary” functions of money] can be deduced from the function of money as a common medium of exchange.”
Any desire to facilitate indirect exchange is always due to uncertainty. As I’m sure you know, if there were certainty, there would be no money; there would only be the numeraire tokens of the ERE. Extreme uncertainty is not qualitatively different from any other degree of uncertainty. The degree of uncertainty always plays a role in the demand for money. But it does so only by virtue of its effect on the relative importance, among other desires, of the individual’s desire to facilitate exchange with a medium of exchange.
Mises, TMC: “The uncertainty of the future makes it seem advisable to hold a larger or smaller part of one’s possessions in a form that will facilitate a change from one way of using wealth to another, or transition from the ownership of one good to that of another, in order to preserve the opportunity of being able without difficulty to satisfy urgent demands that may possibly arise in the future for goods that will have to be obtained by way of exchange.”
So when you talk about “facilitating exchange” and “uncertainty” in terms of components of the demand for money, you’re really talking about the same thing. The degree of uncertainty is nothing but a factor in determining how much an individual wants to hold his wealth in a form that facilitates exchange vs. in a form that facilitates use or “in-house” production. People holding any cash balances whatsoever are always seeking “security”, in that they are always dealing with some degree of uncertainty, and determining the height of their cash balances with reference to that degree of uncertainty. So the (b) component of the demand for money above, is simply part of the (a) component: the desire of people to facilitate exchange by acquiring a medium of exchange.
And the “facility to exchange” that a medium offers is merely another way of saying “purchasing power”. That is why Mises writes:
“The services money renders are conditioned by the height of its purchasing power. Nobody wants to have in his cash holding a definite number of pieces of money or a definite weight of money; he wants to keep a cash holding of a definite amount of purchasing power.”
The demand for money is nothing but the demand for real cash balances, and the demand for real cash balances is nothing but the demand for purchasing power. And again, with any given stock of commodities-to-be-purchased, there is only a fixed amount of purchasing power to go around. So while an individual can increase his purchasing power (sell) by virtue of another individual decreasing his purchasing power (buying), the notion of an entire economy increasing its purchasing power (real, and not nominal, cash balances), either via (1) falling prices or (2) more fiduciary media, is nonsensical. The only way for the total purchasing power (real, not nominal, cash balances) of a whole economy to rise is for the stock of commodities-to-be-purchased to expand.