How are Scandinavian languages related to Old Scandinavian?

Modern Scandinavian languages are the direct descendants of Old Scandinavian, a North Germanic language that emerged as a distinct dialect by the end of the ancient period. During the Viking Age, this language spread across a vast territory, including Iceland, the Faroe Islands, and parts of the British Isles and Russia.1

The relationship between modern languages and their ancestor is defined by both continuity and divergence:

• Dialectal Roots: During the Viking Age, all Scandinavians could communicate easily, but regional orientations led to the development of West Scandinavian (Norway, Iceland, and the Faroe Islands) and East Scandinavian (Denmark and Sweden) groups.12
• Linguistic Evolution: Over centuries, particularly in the late Middle Ages, these groups underwent significant changes in phonology and morphology. For example, while Icelandic and Faroese have remained relatively conservative, preserving features like the case system, other languages simplified their grammar and developed distinct standard forms influenced by urban speech and foreign contact.345
• Phonological Shifts: Modern languages exhibit various shifts from the Old Scandinavian vowel and consonant systems, such as the loss of nasalized vowels and the development of unique pitch or glottalization patterns.4