The two Tocharian languages, Tocharian A and Tocharian B, are closely related and clearly form a branch within Indo-European. Therefore, the discussion of the evidence for the Tocharian branch focuses on the most important changes that have shaped and typologically changed the language. Many innovations of Tocharian, especially in the lexicon, are due to language contact. Some of these contacts took place before the break-up of Proto-Tocharian, while others took place at later stages. It is widely held that, after Anatolian, Tocharian was the second branch to split off the Indo-European proto-language, which may be termed the “Indo-Tocharian” hypothesis. A selection of arguments for Indo-Tocharian from phonology, morphology and lexicon are analysed and evaluated according to the criteria of identifiability, unidirectionality and salience. Although the Indo-Tocharian hypothesis remains attractive, it appears that progress in reconstruction mostly brings Tocharian closer to Core Indo-European than to Anatolian. Tocharian probably split off second, but much later than Anatolian and not long before the remaining speech community started to disintegrate.

The chapter deals with the Indo-Iranian subfamily, its internal division and characteristic features, and its relation to the other subfamilies. While it shows some interesting unique features, it also often agrees with other branches in particular ones. While some of these are common archaisms, sometimes only attested in a few branches due to the different times of attestation, others are innovations, but mostly they can be parallel or part of an areal spread. Thus, no other branch can be clearly shown to be the nearest relative of Indo-Iranian.

The chapter assesses the phylogenetic position of Armenian within the Indo-European language family. After examining the most important, independent developments constituting Armenian as a separate language branch, it discusses those phonological, morphological, and lexical innovations that are shared with, in particular, Greek, Phrygian and Albanian. It then argues that these innovations are sufficiently numerous and significant to posit that together with those languages, Armenian belongs to a higher-order subgroup, Balkan Indo-European.

This chapter discusses the evidence for the existence of an intermediate subgroup Proto-Italo-Celtic, the parent of Proto-Italic and Proto-Celtic. The chapter also examines the connections between Italic and Celtic and the other northwest Indo-European subgroups.

After giving a concise overview of all members of the Anatolian language family, this chapter offers an in-depth discussion of the family’s phylolinguistic make-up. It discusses all major linguistic arguments on the basis of which it can be determined that Anatolian is a single branch within the wider Indo-European language family, as well as the linguistic arguments that can be used for drawing a family tree of Anatolian. It is argued that the first split in the Anatolian branch is between the Hittite branch and a branch that comprises all other Anatolian languages. In the latter branch, first Lydian and then Palaic split off, after which the remaining language develops into Proto-Luwic, the ancestor of the Luwian and Caro-Lycian branches. This phylolinguistic reconstruction of the Anatolian family includes a discussion of the possible dates of all nodes in its tree and of its Proto-Anatolian ancestor language. The chapter also assesses the place of Anatolian within the Indo-European family as a whole on the basis of a discussion of possible closer relationships between Anatolian and other branches of Indo-European, as well as of the Indo-Anatolian hypothesis.

This chapter provides an overview of the main distinguishing features of the Celtic branch of Indo-European. It furthermore discussses the internal relationship between the branches of Celtic, specifically the position of Brittonic. The main arguments in favour of Gallo-Brittonic and Insular Celtic are evaluated.

Since the times of Bopp and Schleicher, Baltic and Slavic have been treated as a single branch of the Indo-European language family. Throughout the nineteenth century, this view remained unchallenged, and it is presented as received wisdom in Brugmann’s Grundriss (1897: 20–1). At the beginning of the twentieth century, however, Meillet (1905: 201–2; 1922: 40–8) challenged the idea of a Balto-Slavic unity and argued that those similarities between Baltic and Slavic that are not archaisms inherited from (dialectal) Proto-Indo-European are due to parallel innovations. Throughout the twentieth century, the matter remained controversial. Balto-Slavic unity was defended by Rozwadowski (1912) and Vaillant (1950: 14), for example, while scholars like Senn (1941; 1970), Fraenkel (1950: 73–112), Pohl (1992), Schmid (1992) and Andersen (1996) remained sceptical and explained the similarities in terms of language contact and convergence.

The chapter presents an overview of approaches to linguistic chronology and subgrouping on a computational basis, along with their roots and a critical discussion, highlighting advantages and drawbacks of the individual methods. The specific results of computational approaches to linguistic chronology and subgrouping are evaluated in the light of current linguistic knowledge. Special focus is given to the potential of applying the computational replication of changes to linguistic subgrouping and chronology. With the use of such method the relative chronology of changes can be established and the exact same set of changes in two languages can be a trace of common development and a subgroup. This is shown on material drawn from different subgroups which are thought to be closely related within Indo-European starting from the most obvious ones (Indo-Iranian) to the ones that are less obvious (Balto-Slavic) and even controversial (Italo-Celtic, Graeco-Armenian). Further potential and problems in the computational replication of changes are discussed at length.

This chapter examines the distinctive innovations uniting Latin, the Sabellic languages and Venetic.

The full range of internal dialect divisions within Indo-European that Albanian potentially enters into are surveyed here and shown to be complex and multifaceted. Nonetheless, it is argued that the overall evidence, based on the criterion of significant shared innovations, points to a particularly close connection between Albanian and Greek. It is further argued that this connection constitutes a subdivision within a discernible Palaeo-Balkanic subgroup that includes Messapic, Phrygian, and Armenian and possibly other fragmentarily known languages. This qualitative assessment of how Albanian fits in dialectally within the larger family matches results reported from computational phylogenetic investigation.

The range of traditional cladistic analysis can be extended greatly with computational methods, but it is necessary to understand how those methods work and what they can and cannot tell us about the diversification of language families. This chapter explores those possibilities and their limits.

This chapter shows how scholars have both justified, and argued against, the subgrouping of Indo-European in the history of the discipline and sets out the justifications given for methodological choices made by researchers. Since the late nineteenth century, it has been generally agreed that the best supporting evidence for reconstructing a subgroup comprising two or more languages is the presence of non-trivial linguistic innovations which have taken place in common during their prehistory, innovations which were not shared by other languages in the same family. This chapter addresses questions which arise out of this methodology, including whether all shared linguistics innovations should be given equal weight in the assessment of possible subgroups, and whether it is possible to reconstruct dialectal variation in a proto-language.