Unless-constructions have often been compared with conditionals. It was noted that unless can in most cases be paraphrased with if not, but that its meaning resembles that of except if (Geis, 1973; von Fintel, 1991). Initially, it was also assumed that, unlike if-conditionals, unless-sentences with counterfactual (or irrealis) meanings are not acceptable. In recent studies by Declerck and Reed (2000, 2001), however, the acceptability of such sentences was demonstrated and a new analysis was proposed.

The present article argues for an account of irrealis unless-sentences in terms of epistemic distance and mental space embeddings. First, the use of verb forms in irrealis sentences is described as an instance of the use of distanced forms, which are widely used in English to mark hypotheticality. In the second part, the theory of mental spaces is introduced and applied to show how different mental space set-ups (in conjunction with distanced forms) account for the construction of different hypothetical meanings. The so-called irrealis unless-sentences are then interpreted as a number of instances of mental space embeddings. Finally, it is shown how the account proposed explains the fact that some unless-constructions can be paraphrased only with if not while others only with except if.