The first part of this paper discusses two important meanings of robustness and shows their essential connection with the notion of intersubjective reproducibility. As I shall maintain, robustness in both senses of the term is intimately connected with the notion of scientific experiment. This is the important element of truth of the mechanistic systems approach, which explains events as products of robust and regular systems and processes. In the second part of this paper I shall show that the concept of robustness of a mechanism, if applied to biological systems, is one-sided and incomplete without a heuristic˗methodical reference to final causes, even though the assumption of the teleological point of view is justified in biology only to the extent that we use it as a counterfactual artifice, capable of bringing to light causal relations which have a robustly reproducible content. In this way, the reflexive, typically human concept of purposefulness may be employed to investigate living beings scientifically, that is, in an intersubjectively testable and reproducible way, to discover mechanisms in living systems which are robust in both senses of the word.