In such cases, the boundaries of the natural kind are vague. Cluster kinds nevertheless do form a kind (Criterion 4 above). Members will have at least some properties in common (Criterion 1). Since the emergence of cluster kinds is not entirely random and a causal-historical account can be provided in virtue of stable homeostatic mechanisms, cluster kinds are sufficiently robust to support induction (Criterion 2) and perhaps even laws of nature in some cases (Criterion 3). Conversely, because th