I prefer “rate of return on capital” to “rate of profit” in part because profit is only one of the legal forms that income from capital may take and in part because the expression “rate of profit” has often been used ambiguously, sometimes referring to the rate of return and other times (mistakenly) to the share of profits in income or output (that is, to denote what I am calling α rather than r, which is quite different). Sometimes the expression “marginal rate” is used to denote the share of profits α.
