According to Kant, something is only a judgement if it is objectively valid. Otherwise, though it might have the grammatical form of a judgement, it does not classify as a 'judgement'. In the Prolegomena, he makes a distinction between 'judgements of experience' and 'judgements of perceptions'. Only the former properly classify as 'judgements' and it is this sense of the term that he mostly uses in the Critique of Pure Reason. This is the reason why Kant criticises logicians who define a judgement as a representation of a relation between two concepts. (cf. B140-141) Allison, following Prauss, interprets the need of judgements being 'objectively valid' as meaning that they must have a truth-value, not that they must be true. This interpretation seems unacceptable as Kant at several places equates objective validity with truth. For example, at A125 Kant explicitly equates objective validity with truth. Furthermore, in the Prolegomena (Prolegomena, 4:298) Kant states that "the objective validity of the judgement of experience signifies nothing else than its necessary universal validity" and states that this signifies that the "judgement agrees with an object", which is equivalent to the definition of truth given at A57/B82. In addition, Kant's classification does not commit him to the absurd conclusion that "every judgement is true, simply in virtue of being a judgement". (Allison: 2004, p. 88) Allison appears to invert the direction of reasoning - it is not that because it is a judgement that it is true, but that only because it is true that it classifies as a judgement. This implies that there are no false judgements in the sense that nothing that is false will classify as a 'judgement', but this does not bring with it the absurd conclusion that there can be no error.
A similar method of classification can be seen to be at work with respect to the notions of 'experience' and 'imperative'. The way Kant uses the term 'experience' differs from contemporary usage insofar as experience, understood in its modern usage, must be objectively valid in order to classify as 'experience' in Kant's sense. This can be seen when looking at the Transcendental Deduction since it is a strong notion of experience that constitutes the starting point of the Deduction. (cf. Ameriks: 1978) Similarly, every imperative can be expressed as an ought-statement but this does not imply that every ought-statement is an imperative. While all ought-statements are grammatical imperatives, they are not necessarily 'imperatives' in Kant's sense as these are universally valid principles that are necessitating for the will (this includes both hypothetical and categorical imperatives - the former are hypothetically necessitating, whereas the latter are categorically necessitating). Thus, there can be formulations that have the grammatical form of imperatives, such as imperatives of etiquette, without necessitating the will and, accordingly, such statements do not classify as 'imperatives'. We can thus see that Foot's criticisms are misplaced when she says that "[i]t follows that if a hypothetical use of 'should' gave a hypothetical imperative, and a non-hypothetical use of 'should' a categorical imperative, then 'should' statements based on rules of etiquette, or rules of a club would be categorical imperatives." (Foot: 1972, p. 309) No matter what form the should-statement has and no matter how it is used, it only expresses a categorical imperative if it is an objective principle that necessitates the will.