  Let us first examine the subjunctively defined baselines (1)-(3). Determining whether redistribution occurred relative to each of these baselines can be extremely difficult in practice, since the counterfactuals upon which they depend are quite complex. This is not always adequately recognized. It is sometimes assumed, for example, that baseline (2) is identical to the pattern of gross (pre-tax) incomes, so that difference between gross and net income will count as redistributed income according to it. But this is mistaken. The presence or absence of income tax will itself substantially influence many market outcomes, including the availability of economic opportunities to persons with different sets of skills and personal characteristics, and the gross incomes that can be earned in different jobs. Had no income tax been in place, altogether different jobs and economic opportunities would most likely have existed, and gross incomes would most likely have been very  different.[8]  Indeed, it is extremely hard even to venture a guess at what distribution of income would have obtained had there been no income  tax.[9]  Identifying the set of holdings that would obtain in the subjunctive baseline scenario invoked by (3) is even more problematic. This is because there is no obvious way of determining how much some individual has contributed to production. Even examples that involve one person producing something from a set of raw materials without the help of others — it is not obvious how to separate out how much of the produced good is due to Crusoe’s contribution and how much to the materials themselves. In cases of interdependent production, things become even more difficult, since there is usually no non-arbitrary way of determining the contributions of different factors of production (for example, labor, capital, raw materials, so-called public goods, and so on) that jointly lead to total output. It is sometimes claimed that using a person’s marginal product as a proxy for what they have contributed to production can circumvent these problems. But this, too, is mistaken.  First, in conditions where there are increasing or decreasing returns to scale, not everyone will be able to receive what they contribute.  Where there are increasing returns to scale, for example, it will be impossible for people to receive what they contribute at the margins since the marginal return is greater than the average. Second, while assessments of the marginal productivity of different inputs can be useful for deciding how to use additional resources so as to maximize profit, they do not show how much each resource has produced as a proportion of the total output.