But there are others models which can. SylL is one of them. SylL is a model displaying the 'categorical' or 'categorial' or 'predicative' structure of sentences. SylL is concerned only with what PropL would categorize as simple sentences. Rather than diplaying truth-functionality as the salient characteristic, SylL takes categoriality as salient.
All gray objects swim.
So, All whales swim. All whales swim Trans. So, according to PropL, the argument is invalid. But, SylL CAN show us that. And that, among other reasons, is why we study such a model.