He was educated at Bonn and at Jena where he studied philology (historical linguistics) with August Schleicher and specialized in Indo-European, especially Slavic, languages.

In Bonn he published the work Die Verwandtschaftsverhältnisse der indogermanischen Sprachen ('The Relationships of the Indo-Germanic Languages', 1872), which presented his Wellentheorie ('wave theory').

According to this theory, new features of a language spread from a central area in continuously weakening concentric circles, similar to the waves created when a stone is thrown into a body of water.

The theory was directed against the doctrine of sound laws introduced by the Neogrammarians in 1870, and contrasted with Schleicher's phylogenetic model.

He was joint editor with Ernst Kuhn of the Zeitschrift für vergleichende Sprachforschung (Journal for Comparative Language Research) from 1875 until 1901.