In some cases, cognate terms used for parallel practices in the early medieval Irish and Welsh laws allow us to assume that these practices were already used in what is referred to by linguists as the 'common Celtic period', which is usually dated to around 1000 BC (e.g. Kelly 1988, 231), although this at best is a very rough estimate. Where parallels for such practices exist, but with non-cognate terminology, in other Indo-European laws, we can start to consider the cognate practices as specifically Celtic forms of law. Similarly, where such cognate terminology exists for parallel practices in the early medieval Celtic laws, but not in other Indo-European laws, we can consider these to be specifically Celtic laws.