People have long speculated that their languages came from a single source; during the Renaissance, for example, scholars noted that languages seemed to group themselves in the ways they said "god": Latin deus, Spanish dios, vs. Swedish gud, English god, vs. Russian and Polish bog, etc. As early as 1767, physician James Parsons collected numbers from many European languages, as well as those of Iran and India, and found them to be quite similar; he concluded that they must have all come from one source: Noah’s Ark. But Sir William Jones, Chief Justice of India, took this observation a step further. As an educated man, he was trained in the classical languages, so that when he went to India and began to examine Sanskrit, he saw right away how similar it was to Greek and Latin, not only in vocabulary, but even in inflections and grammatical features. His address to the Bengal Asiatic Society in 1786 contained the first clear assertion of the existence of Proto-Indo-European:   The Sanskrit language, whatever be its antiquity, is of a wonderful structure; more perfect than the Greek, more copious than the Latin, and more exquisitely refined than either, yet bearing to both of them a stronger affinity, both in the roots of verbs, and in the forms of grammar, than could possibly have been produced by accident; so strong, indeed, that no philologer could examine them all three, without believing them to have sprung from some common source, which, perhaps, no longer exists. Building upon this observation, Rasmus Rask said that scholars had to do more than just use intuition to set up a proto-language; they had to find regularities and systematic developments. For example, he noticed that certain sounds in Greek (e.g., ph, as in phrater ‘brother’ and phero ‘I carry’) corresponded regularly to other sounds in Germanic (e.g. b, as in Eng. brother and bear). Jacob Grimm, famous as a collector of fairly tales, was the first to publish a systematic explanation of how Germanic must have diverged, in extremely consistent ways, from the proto-language. His explanation is now called "Grimm’s Law."

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