This paper examines an intertemporal optimizing consumer or a representative consumer-firm in a deterministic setting subject to a general (either linear or nonlinear) capital accumulation equation. Duality theory is used to recast the Hamilton–Jacobi equation for dynamic optimization in terms of an instantaneous and an intertemporal profit function. An envelope theorem allows derivation of an explicit solution for the value of the costate variable as a function of the state and other variables. The final model form only requires specification of atemporal functions that are linked into a closed-form solution for the optimal dynamic decision variables through a system of contemporaneous simultaneous equations.

Marshallian demand, supply, and entry models are employed for major sectors of an economy that can be combined with factor market models for money, labor, capital, and bonds to provide a Marshallian macroeconomic model (MMM). Sectoral models are used to produce sectoral output forecasts, which are summed to provide forecasts of annual growth rates of U.S. real GDP. These disaggregative forecasts are compared to forecasts derived from models implemented with aggregate data. The empirical evidence indicates that it pays to disaggregate, particularly when employing Bayesian shrinkage forecasting procedures. Further, some considerations bearing on alternative model-building strategies are presented using the MMM as an example and describing its general properties. Last, data requirements for implementing MMMs are discussed.

Karl Shell is without a doubt one of the central players in the development of economic theory and macroeconomics in the latter part of the twentieth century. He has made important contributions on topics ranging from growth theory, to overlapping generations, to extrinsic uncertainty, to monetary economics, to market games, and to technological innovation. His collaborations with Dave Cass are legend, and include the seminal formulation of the concept of sunspot equilibria. His “Notes on the Economics of Infinity,” and his papers with Yves Balasko are overlapping-generations classics. Shell's many coauthors read like a Who's Who in economics, and include (in no particular order) Joe Stiglitz, Franklin Fisher, Miguel Sidrauski, Ned Phelps, Duncan Foley, Walt Heller, Albert Ando, Jim Peck, Rod Garratt, Aditya Goenka, Christian Ghiglino, and Todd Keister. This is also a club to which we are also proud to belong.

Shell's research is first rate and highly innovative, but his full contribution to economic theory must also be judged by his long service as the editor of one of the profession's premier journals, the Journal of Economic Theory. As the founding editor of JET, Shell took a small upstart journal, originally envisioned as a niche outlet for papers on mathematical economics, and turned it into one of the best in the profession. JET has published papers that have had major impacts on the development of economic theory in all its various flavors.

Because of Shell's long stewardship of JET, the story of his professional life—which we hope we have captured in this interview—is also a history of the evolution of economic theory over the past quarter century. We spoke with Karl in his office at Cornell University and over lunch at the faculty club in the Statler, and the interview tapes we made were very much a three-way conversation between Karl and the two of us. In editing the transcripts of these tapes for publication, we wished to keep the focus of the conversation on Shell, and have therefore adopted the same anonymous “MD” moniker we used in our interview of Dave Cass to mask the identity of the questioner. We hope you enjoy the conversation as much as we did.

We analyze the role of intrafirm bargaining in the large-firm matching model and underline the conditions under which the Pissarides equivalence between this model and the “single-worker” firm's model holds.

We investigate the size and power properties of the AH test of evolutionary change. This involves examining whether the size results are sensitive to both the number of individual frequencies estimated and the spectral shape adopted under the null hypothesis. The power tests examine whether the test has good power to detect shifts in both spectral position (variance) and spectral shape (autocovariance structure).