As is well known, the Insular Celtic languages (Irish, Scots Gaelic, Welsh, Breton and the now-extinct Manx and Cornish) utilize a class of verbal abstracts known as "verbal nouns" to perform the functions that are fulfilled in other Indo-European languages by infinitives and supines. Yet in many ways the Celtic verbal noun remains somewhat of an enigma. The purpose of the present study is to examine the historical morphology of the verbal noun in the earliest Celtic language for which we have a meaningful literature, namely Old Irish, in order (1) to distinguish the derivational patterns that lie behind their multifarious formations, and (2) to clarify the place of the Celtic verbal noun within the development of Indo-European. Twenty-six early Old Irish texts were perused for their verbal nouns, dating from the seventh century through the first half of the eighth (some in contemporary manuscripts, others existing only in later copies) and covering a range of genres including textual glosses, prose, poetry, and law. The almost 650 tokens of verbal nouns that emerged from this search were used as the basis for the analysis and conclusions of the study.

In addressing the problem of defining the Old Irish verbal noun, a multifaceted approach is advocated in order to capture the systemic character of the verbal noun, taking into consideration the interplay of morphological, semantic, and syntactic factors. It is concluded that the verbal noun, while possessing limited verbal features, is not infinitival in Old Irish; it is primarily and fundamentally a substantive, distinguishable from an ordinary abstract only in certain aspects that depend on the special associative relationship it has with its verb.

The body of the study concentrates on morphological concerns. An overview of the rather complicated system of Old Irish verbal compounding is presented first, as this is also reflected in the verbal nouns; and a discussion of verbal-noun formation follows. Five types of verbal nouns can be discerned in Old Irish, based on the derivational relationship each bears to its verb: (1) deradical formations corresponding to primary verbs; (2) deverbative formations, mostly from secondary verbs; (3)source nouns of denominative verbs; (4) deadjectival formations to cognate factitive verbs (also denominative formations to cognate denominative verbs); and (5) suppletive verbal nouns. The more than two dozen formative suffixes that characterize the derived verbal nouns have unmistakable Indo-European origins; each of these is examined briefly.

In the exposition of the data, the morphological details of all the verbal nouns that make up this study, organized according to the verbal root with which they are associated, are systematically analyzed in accordance with the above framework. The accompanying commentary covers sundry issues of etymology, historical phonology, morphology, semantics, and any other details of interest elicited by the material.

The concluding chapter considers the placement of the Celtic verbal noun within the wider Indo-European context in the light of these findings. While some previous studies have posited the existence of infinitival formations in the Indo-European proto-language and have concluded that the verbal noun of the Insular Celtic languages must be an innovation, it is argued here that the broad alignment of primary verbal nouns with primary verbs and secondary verbal nouns with secondary verbs, which is systematic in Old Irish, is best explained in terms of inheritance. This implies that Proto-Indo-European itself possessed only verbal nouns, and that the infinitival formations of the daughter languages must have arisen independently.