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Over the last 50 years, much interests been focused on preferential flows including macropore, finger and funnel flows and many important progress have been made. In this article, finger flows are classified into two types according to their respective physical mechanisms, i.e. finger flows of type I - preferential flows in homogeneous continuum media with randomness in initial conditions - and finger flows of type II - preferential flows in inhomogeneous continuum media. It is argued that in both cases Darcy’s law should always hold which plays an important role in the physical interpretation for the finger formation (with random modifications in soil potential in the case of type II). In contrast to the classification of finger flows, macropore flows are preferential flows in discontinuous media, and the concept of random potential might equally well applicable to these cases.