Why are proposed links between Austronesian and Indo-European languages considered speculative?

Proposed links between Austronesian and Indo-European languages are considered speculative because they lack the rigorous evidence required to establish a genetic relationship in comparative linguistics.1

To prove that languages are genetically related, linguists must demonstrate systematic matches in phonology, vocabulary, and grammar that cannot be attributed to chance or previous contact between unrelated groups. While scholars such as Franz Bopp and Renward Brandstetter explored potential connections in the 19th and early 20th centuries, these proposals have not achieved a general following among linguists.21

In the field of historical linguistics, such hypotheses are often viewed as speculative because they fail to meet the strict criteria of the comparative method, which relies on reconstructing a common protolanguage through recurrent, verifiable sound correspondences. Consequently, while many external relationships have been proposed for the Austronesian family based on geographic proximity, most remain unproven and lack broad academic consensus.12