 From the obvious existence of mediated judgments, however, it follows that there must also be immediate judgments (WL III, 125, 138–139). Immediate judgments cannot be false and must therefore be certain (WL III, 212, 229, 263). Certainty has thereby not to be taken in its objective sense in which a proposition \(s\) is certain relative to a set \(\sigma\) of propositions iff the logical probability of \(s\) relative to \(\sigma\) is 1, i.e., iff \(s\) is a logical consequence of \(\sigma\) (WL II, 173). In the present context, certainty must rather be taken in a subjective sense in which it is primarily a property of a judgment; if two judgments grasp one and the same proposition, one of them can be certain (in this subjective sense of the term) whereas the other one is not (WL III, 263 f.). As the two most important kinds of immediate judgments among the empirical ones Bolzano mentions judgments of the form “I — have — an appearance \(X\)” and “That (what I just now perceive of) — has — property \(b\)” (WL I, 181, WL III, 131, 139, 229). Judgments of these two kinds are called ‘(immediate) perceptual judgments’, whereas the term ‘empirical judgment’ is normally used only for mediated judgments containing a subjective intuition (WL III, 131 f.). The propositions “grasped” by these immediate perceptual judgments are empirical propositions whose subject ideas are intuitions that are usually expressed by means of the indexicals ‘I’ and ‘that’. Bolzano’s philosophy of science can thus be found to be empiricist, founded on a phenomenalist basis.