就语形方面，凯尔特语的名词与形容词与其上层语并无什么显著的改变，但相较于其他实存的印欧语言，海岛凯尔特语的动词就拥有一种独特且未解的特征：其动词的词形变化会随著该动词是否位于一个句子的绝对首位（海岛凯尔特语为动主宾即 VSO 语言）或该动词之前是否有一个动词前置质词而有所不同。这样的特色在古爱尔兰语中表现得最为突出，但在后来的苏格兰盖尔语和中古威尔斯语里也有一些相同的例子。
Hammarström, Harald; Forkel, Robert; Haspelmath, Martin; Bank, Sebastian (编). Celtic. Glottolog 2.7. Jena: Max Planck Institute for the Science of Human History. 2016.
Ball, Martin J. & James Fife (ed.) (1993). The Celtic Languages. London: Routledge. ISBN 978-0-415-01035-1.
Borsley, Robert D. & Ian Roberts (ed.) (1996). The Syntax of the Celtic Languages: A Comparative Perspective. Cambridge: Cambridge University Press. ISBN 0521481600.
Cowgill, Warren. The origins of the Insular Celtic conjunct and absolute verbal endings. H. Rix (ed.) (编). Flexion und Wortbildung: Akten der V. Fachtagung der Indogermanischen Gesellschaft, Regensburg, 9.–14. September 1973. Wiesbaden: Reichert. 1975: 40–70. ISBN 3-920153-40-5.
Celtic Linguistics, 1700-1850 (2000). London; New York: Routledge. 8 vol.s comprising 15 texts originally published between 1706 and 1844.
Forster, Peter and Toth, Alfred. Towards a phylogenetic chronology of ancient Gaulish, Celtic and Indo-European PNAS Vol 100/13, July 22, 2003.
Gray, Russell and Atkinson, Quintin. Language-tree divergence times support the Anatolian theory of Indo-European origin Nature Vol 426, 27 Nov 2003.
Hindley, Reg (1990). The Death of the Irish Language: A Qualified Obituary. London; New York: Routledge. ISBN 978-0-415-04339-7.
Lewis, Henry & Holger Pedersen (1989). A Concise Comparative Celtic Grammar. Gottingen: Vandenhoeck & Ruprecht. ISBN 978-3-525-26102-6.
McCone, Kim. The PIE stops and syllabic nasals in Celtic. Studia Celtica Japonica. 1991, 4: 37–69.
McCone, Kim. Relative Chronologie: Keltisch. R. Beekes, A. Lubotsky, and J. Weitenberg (eds.) (编). Rekonstruktion und relative Chronologie: Akten Der VIII. Fachtagung Der Indogermanischen Gesellschaft, Leiden, 31. August–4. September 1987. Institut für Sprachwissenschaft der Universität Innsbruck. 1992: 12–39. ISBN 3-85124-613-6.
Russell, Paul (1995). An Introduction to the Celtic Languages. London; New York: Longman. ISBN 978-0-582-10082-4.
Schmidt, K. H. On the reconstruction of Proto-Celtic. G. W. MacLennan (编). Proceedings of the First North American Congress of Celtic Studies, Ottawa 1986. Ottawa: Chair of Celtic Studies. 1988: 231–48. ISBN 0-09-693260-0.
Schrijver, Peter. Studies in British Celtic historical phonology. Amsterdam: Rodopi. 1995. ISBN 90-5183-820-4.
