That first-unit demand conforms to the characteristics of proportionate effect must be regarded as an axiom. A plausibility argument is provided here. Let mj = Ï†(mj-1) with mj the number of monetary units to which one is indifferent relative to the first unit of a phenomenon on the j'th day of that person's life. We want to show that Ï†(mj-1) = (1+Îµj)mj-1. Consider a man who wants to take out a loan at interest. He must think he will have more money in the future than he does now. (More money holdings, not necessarily more wealth.) If he does, the value of individual monetary units will tend to decrease over time relative to other phenomena; that is, Ï† is a positive function when averaged over all phenomena. To determine how much interest he is willing to pay, the man must specify this average Ï†. For him to calculate the interest owed per unit of time as a percentage of the principle is equivalent to specifying Ï†(mj-1) = (1+Îµ)mj-1 with Îµ > 0 fixed. Fixing Îµ is a special case of Îµj being a random variable. Here, the probability density function is unity at Îµ and zero elsewhere. Thus, the axiom that first-unit demand conforms to the characteristics of proportionate effect is a generalization of calculating interest as a percentage of the amount owed. In fact, this is how people have calculated interest throughout recorded history, although economics having always been a soft science, they never asked for proof. Perhaps the value of money decays harmonically over time or in another way besides exponentially? This question is addressed in *Axiomatic Theory of Economics*, but for now let us proceed to investigate the consequences of people's points of indifference for their first unit of each phenomenon being lognormally distributed.