Substance and semantics: The question of capital

The perennial question 'What is Capital' has been getting some attention recently. Although the distinction between capital as a financial construct and capital as a collection of physical production-goods is well known, we argue that the former concept is undepreciated. The two concepts are often conflated in practice, and the relationship between them is seldom well understood. We spell out the financial concept of capital emphasizing its importance as an indispensable instrument of calculation and accounting. We consider some views of human, social and other capital and how we differ from them. We present reasons for rejecting the notion of an aggregate production function in standard growth theory (which uses the notion of an aggregate stock of physical capital) and as recently used by Thomas Piketty in his well-known work.