Cross-linguistic comparison of unrelated or distantly related languages is often hindered by the lack of a one-to-one correspondence between the formal repertoires of the different languages. This article presents an example of such a situation, where the comparison of the Irish and Italian prepositional inventories is made impossible, on a formal basis, by the different sizes of the two sets of forms and the different semantic segmentation of the spatial-content continuum, i.e., the fact that one and the same form can express different concepts in a way that is cross-linguistically not always valid, and – conversely – that one and the same concept may be expressed by more than one linguistic form in a language and by just one in the other. A possible way of tackling this problem for the case at hand, based on a conceptual rather than formal comparison, is subsequently expounded. The aims of the comparison in point, that is, finding patterns of metaphorical sense extensions in the domain of Irish and Italian prepositions, are also explained.