"2 + 2 = 4" is an objective fact if we agree on the fact that "+" signifies the operation of addition and not, let's say, string concatenation, which will result in "2 + 2 = 22".

The crux of the matter is that we no longer have a basis of facts on which to rely, to provide a cohesive story for the Kantian questions: what can I know? what ought I to do? what may I hope for? what is man?. One might even argue that we never had [1].

[1] Bruno Latour, We Have Never Been Modern