A common fallacy presents Hebrew usage in first century Judea and the Galilee as a strictly sacred, literary language, comparable to Latin in Medieval Europe. The notion that both Hebrew and Latin were monolithic is erroneous. During the Second Temple period, Hebrew had developed into two social dialects. The high register was a literary dialect used for prestigious communication, known today as “Late Biblical Hebrew,” the language of books like Ezra and Nehemia and much of the Qumran writings. The low register can be seen in works like the Copper Scroll from Qumran Cave 3, and in various papyri, graffiti, and inscriptions from the Second Temple period, as well as the tannaitic and amoraic writings of rabbinic literature. Already in 1908, M.H. Segal had pointed out to the scholarly world that Mishnaic Hebrew showed the marks of the internal development of a colloquial language - it was definitely not an artificial usage by a scholarly elite.Dr. Buth is an expert Aramaist and his thoughts are always worth listening to. I think some of the arguments above are more persuasive than others. The last points out rightly that we have next to no direct information about the languages spoken in the Galilee in the first century. But this point applies to the argument about parables. The language pattern of parables in the much later rabbinic texts doesn't necessarily tell us anything about the language Jesus used to tell parables in the first century.
Secondly, it is argued that first century Judean and Galilean Jews needed a translation of the Hebrew Bible, the Aramaic Targums. The argument runs that the existence of the Aramaic Targums must mean that the people did not know Hebrew. However, the Targums served an interpretive interest beyond simple translation, a commentary that elucidated and expanded the plain text. Also, although many Aramaic writings are found among the Qumran community’s scrolls, except for the foreign (imported) Job and a potential text for a pilgrimage holiday, there is no Aramaic Bible. The Targum traditions that we have stem from the 2nd and 3rd century C.E. At this point in time, a widespread, first-century Aramaic Targum practice in Israel remains speculation and the evidence available, meager though it is, actually points away from such an assumption.
Parables are the third piece of the linguistic puzzle. Certain Jewish literary genres were always in Hebrew, one of which was the rabbinic story parable. In rabbinic literature, even within Aramaic contexts, the story parable was always given in Hebrew. The potential connection with Jesus is obvious, since Jesus, too, is frequently characterized as someone who taught the populace in parables. The parable genre was used for making a point that could be readily grasped by all levels of society. They were a popular literary genre, not “highbrow” or “elitist.”
Archaeology has also been heralded as decisive evidence in the Aramaic-only Jesus. According to Gilad: “In the Galilee, where Jesus lived, Aramaic had taken over by the time Jesus was born. In the south, in Judea, archaeological evidence shows that some pockets of Hebrew still remained during the first century C.E.” This is ironic. The real problem is that we have virtually no archaeological evidence for first century Semitic (Aramaic or Hebrew) languages in the Galilee. We do have Galilean names found in the south, and they are Hebrew!
If the book of Job had a foreign origin, this would scarcely have been important in the first century or a reason to make a Targum of it and not other books. I suppose one could say that the Hebrew of Job is just really difficult and that could make a Targum desirable — but why an Aramaic translation rather than just a paraphrase into easier Hebrew? Also 4Q156 preserves fragments of what looks like a Targum to the book of Leviticus, although this is debated. I would say that the Targum of Job does at least hint that there were elements of the population who were more comfortable studying the Bible in Aramaic than in Hebrew.
The strongest argument is the evidence for diglossia (the presence of a high-class literary dialect and a colloquial dialect) in Hebrew going all the way back to the Hebrew Bible, and I should have taken this into account in my earlier comments. Most of the Bible is written in the literary dialect, whereas Mishnaic Hebrew is the colloquial dialect now raised to literary status. It is an inference, but a persuasive one, that Hebrew continued to be spoken in the Second Temple period and that the Mishnah adopted this spoken dialect for literary use. Who exactly continued to speak Hebrew (Judeans? Galileans? Both? At what social level?) is perhaps not entirely clear, but this does offer some good additional evidence that Jesus spoke both Aramaic and Hebrew.
For more on diglossia, see Gary A. Rendsburg, Diglossia in Ancient Hebrew (New Haven, CT: American Oriental Society, 1990).