What significant development marked the beginning of Modern English?

The significant development that marked the beginning of Modern English is the invention of the printing press. This invention, attributed to Johannes Gutenberg in the mid-15th century, revolutionized the way information was disseminated. As books became more accessible and affordable, literacy rates increased, leading to a greater standardization of language. The printing press allowed for the widespread distribution of texts in English, which helped solidify its grammar, spelling, and vocabulary, distinguishing Modern English from its earlier forms.

While other events like the Great Vowel Shift and the influence of the Christian missionaries played essential roles in the evolution of the English language, they do not signify the onset of Modern English in the same transformative way as the printing press. The printing press facilitated the exchange of ideas and dialects, accelerating the transition into a new linguistic phase, supporting the development of a more unified English language that we recognize today.