How do we know the Hebrew language? It is the language of the Hebrew Bible. How do we know the text of the Hebrew Bible? We have a bunch of manuscripts, the oldest (the Leningrad Codex, the Aleppo Codex, the Cairo Codex) being about 1000 years old. They are written in a consonantal script with dots indicating the vowels and aspects of the pronunciation of consonants. There have been three systems for these dots (with variations) invented in the late first millennium CE in Tiberias, in Babylon and in Jerusalem. They are different from each other, but we don't know if these differences are due to dialectal differences in the pronunciation of a living language, or differences in the prescriptive pronunciation of a dead language. Around 300 to 100 BCE in Alexandria, the Bible was translated into Greek, with personal names and place names transliterated from the Hebrew; the consonants more or less agree with the dotted manuscripts but the vowels don't (assuming that our understanding of the pronunciation of Ancient Greek is correct). Adam's wife is named Khavva in dotted Hebrew and Eua in the Greek translation. There was also a 3rd century CE transliteration of the Hebrew Bible into Greek written side by side with several translations; fragments of this work are preserved; the Hebrew is different from both the dotted version and the Greek translation, but the Greek text has many mistakes and it is possible that the differences in Hebrew are also mistakes. The Dead Sea Scrolls are about 1000 years older than the manuscripts with the dots; they make heavier use of consonants that stand in for vowels than is the rule in Biblical Hebrew (or Modern Israeli Hebrew, for that matter). The second-person singular possessive suffix is "-k" in undotted writing; with the dots it is "-ka" for the masculine and "-ak" for the feminine; in the Dead Sea Scrolls, the masculine suffix is also "-ka", which confirms the authenticity of the dots. Curiously, Exodus 13:16 also has "-ka"; the verse seems to be a later copy of Exodus 13:9. On the other hand, the Greek transliteration always has the final "-kh". However, the second person plural masculine personal pronoun is "atem" in dotted Hebrew and "atVma" (where V is an unknown vowel) in the Dead Sea Scrolls. We don't know if this reflects a different dialect of Hebrew or a mistake on the part of the inventors of the dots.