The theory and practice of contemporary comparative biology and phylogeny reconstruction (systematics) emphasizes algorithmic aspects but neglects a concern for the evidence. The character data used in systematics to formulate hypotheses of relationships in many ways constitute a black box, subject to uncritical assessment and social influence. Concerned that such a state of affairs leaves systematics and the phylogenetic theories it generates severely underdetermined, we investigate the nature of the criteria of homology and their application to character conceptualization in the (...) context of transformationist and generative paradigms. Noting the potential for indeterminacy in character conceptualization, we conclude that character congruence (the coherence of character statements) relative to a hierarchy is a necessary, but not a sufficient, condition for phylogeny reconstruction. Specifically, it is insufficient due to the lack of causal grounding of character hypotheses. Conceptualizing characters as homeostatic property cluster natural kinds is in accordance with the empirical practice of systematists. It also accounts for the lack of sharpness in character conceptualization, yet requires character identification and re-identification to be tied to causal processes. (shrink)