This paper extends Lucas (1978) to a production economy with two capital goods. It is an RBC model in which each unit of investment requires a new idea, an "option". When options are scarce, new capital is harder to put in place and the value of old capital rises. Thus the stock market and...

Investment of U.S. firms responds asymmetrically to Tobin's Q: Investment of established firms -- `intensive' investment -- reacts negatively to Q whereas investment of new firms -- `extensive' investment -- responds positively and elastically to Q. This asymmetry, we argue, reflects a...

"Growth of technological variety offers more scope for the division of labor. And when a division of labor requires some specific training, the technological specificity of human capital grows and, with it, probably the firm specificity of that capital. We build a simple model that captures this...