and Δ such that for an arbitrary positive number δ$_{1}$ and for each solution η$_{x}$$_{(}$$_{t}$$_{)}$ ( t, y$_{0}$ ) , there exist an interval J 1 ⊂ [0 , ∞ ) , with a length no less than Δ , and a solution η$_{x}$$_{(}$$_{t}$$_{)}$ ( t, y$_{1}$ ) such that ‖ y$_{0}$ − y$_{1}$ ‖ < δ$_{1}$ and ∥ η$_{x}$$_{(}$$_{t}$$_{)}$ ( t, y$_{0}$ ) − η$_{x}$$_{(}$$_{t}$$_{)}$ ( t, y$_{1}$ ) ∥ > ϵ$_{1}$ for all t ∈ J $^{1}$. Moreover, we say that system (2.2) is chaotic if it replicates the sensitivity of (2.3) and the coupled system (2 . 3) + (2 . 2) possesses infinitely many unstable periodic solutions in a bounded region. Next, we will formulate a theorem that forms the mathematical basis of the paper. The following conditions are required: (C1) System (2.1) admits a non-constant and orbitally stable periodic solution; (C2) System (2.3) possesses sensitivity and is chaotic through period-doubling cascade; (C3) The functions B and G are bounded; (C4) There exists a positive number L$_{B}$ such that for all z$_{1}$, z$_{2}$ ∈ R $^{n}$; (C5) There exists a positive number L$_{ψ}$ such that The following assertion is based on the results in [9]. for all x$_{1}$, x$_{2}$ ∈ R $^{m}$. Theorem 2.1 If conditions ( C 1) − ( C 5) hold and | ε | is sufficiently small, then there exists a neighborhood U of the orbitally stable limit cycle of (2.1) such that solutions of (2.2) which start inside U behave chaotically around the limit cycle. That is, the solutions are sensitive and there are infinitely many unstable periodic solutions. In what follows, we will require regular systems, that is, models with asymptotically stable equilibria or limit cycles, that can be perturbed to generate chaotic business cycles. In this part of the paper we propose three economic models to be used as base systems. ‖ B ( z$_{1}$ ) − B ( z$_{2}$ ) ‖ ≤ L$_{B}$ ‖ z$_{1}$ − z$_{2}$ ‖ , ‖ ψ ( x$_{1}$ ) − ψ ( x$_{2}$ ) ‖ ≥ L$_{ψ}$ ‖ x$_{1}$ − x$_{2}$ ‖ , 3 Economic Models: The Base Systems 7