Strong positivism insists, from one point of view, that unless we have a theory of everything X we don't know anything relevant about X. (Another point of view is that it insists that anything not expressed in our theory of everything X is irrelevant, which amounts to the same thing). I've talked before about how the positivist-postmodern dynamic works out in practice: positivists believe (contra all evidence and reason) that we can formally express everything true (or relevant) about X. Postmoderns conclude that because positivism is irrational we don't really know anything about X. Both positivism and postmodernism, then, depend on a particular approach to knowledge: an approach which insists that completeness is required in order to have relevant knowledge at all; that incomplete knowledge is invalid. In a sense, then, they both confuse the incomplete with the indefinite.
Modernity exists in a stew of positivism and postmodernism. Because of this, arguments often proceed as though definite conclusions cannot be reached until a comprehensive definition or "Theory of Everything X" is produced.
But we don't need to have a Theory of Everything in order to know some things. For example, we don't need to have a Theory of Everything Abortion to know that when a woman has the living child suctioned out of her womb because she doesn't want to get fat, she has procured an abortion. And we don't need to have a Theory of Everything Torture in order to know that when we waterboard a prisoner to get him to talk, we have committed an act of torture. Sure, stating what was done in that manner doesn't fit a careful and formal deontological casuistry of the morality of acts, and it doesn't provide us with a Theory of Everything with respect to the moral subject matter in question. But that doesn't mean we are even slightly uncertain as to whether what was actually done in the particular case was abortion or torture.