Early theoretical investigations into initiation of limestone cave development suggested that water entering small fractures approaches saturation within a short distance and thus appeared to be unable to produce much further enlargement of these fractures. The answer to this problem seems to be White's (1977) ''kinetic trigger'' idea, emphasizing the precipitous drop in dissolution rates as equilibrium is approached. However, minimum conditions of the flow rate, passage geometry, and initial CO2 concentration may exist, below which the waters will so nearly achieve saturation that caves will be unable to develop. Modeling results indicate that under geologically reasonable PCO2 and head gradient values, the minimum initial aperture widths in which caves will develop is of the order of 100 &mgr;m. Initial apertures wider than about 500 &mgr;m will form passages very easily, even under low head gradients. There will thus be strong differential selection among initial flow paths with regard to cavern passage development.