Did Jesus speak Greek or Aramaic?

When Alexander the Great conquered the known world about 300 BC, he made Greek the official language of his empire, as well as enforcing a common form of currency. This Greek came to be known as Koine Greek, (pronounced "koy-NEY") which means "Common Greek". With a common language and common currency, trade was greatly facilitated. Koine Greek was still the working language of the Roman Empire in the 1st century. Certainly if you were a literate person, or a businessperson, there were very compelling reasons to know Greek.

So it was very common in the first century Roman Empire for your own local native language to be your main tongue, but Greek as a second language.

Many of the Jews of the Diaspora ("the scattered" �- those scattered outside of Palestine throughout the Empire) no longer knew Hebrew, and used the translation of the Old Testament called the Septuagint, which was in Greek. This was the Greek Old Testament from which Paul and other New Testament writers quoted.

It was because Greek was such a common second language that Paul was able to travel the Empire and be understood wherever he preached. This enormously facilitated his efforts to spread Christianity.

And it could be argued that because Palestine was a major crossroad in the ancient world, it would make knowing Greek all the more compelling—what with all the non-Aramaic speaking foreigners passing through all the time.

As to whether Jesus used Aramaic or Greek in his utterances: we just don't have enough hard facts to know for a certainty. There is every reason to believe that Jesus would know Greek as a literate man of his day (as well as Aramaic which was native to that area). And Palestine being the crossroads that it was, it seems entirely logical that he would preach in Greek so as to be understood by the greatest number of people. The simple language of his parables, for example, would have worked very well with audiences trying to understand him in a second language.

And then there's the internal evidence where Jesus does use Aramaic and it is recorded by the Gospel writers. Here are passages where an Aramaic word or phrase occurs in the middle of the Greek (in the Gospels), by Jesus or anyone else:

(Jesus:) "And whoever says to his brother: Raka..." ( Matt.5:22).
(Jesus:) "And having laid hold of the child's hand he says to her: Talitha koum, which is being translated: Maiden" ( Mark.5:41)
(The Gospel Writer:) "And they lead him up to the place Golgotha, which is being translated Place of the Skull." ( Mark.15:22)
(Jesus:) "And in the ninth hour Jesus cried out with a loud voice: Eloi, Eloi, lama sabachtani, which is being translated: My God, my God, why have you abandoned me?" ( Mark.15:34)
(Followers:) "Now when Jesus turned and saw them following he says to them: What are you seeking? And they said to him: Rabbi, which is saying being translated: Teacher..." ( John.1:38)
(Followers:) "This one finds first his own brother Simon and says to him: We have found the Messiah, which is being translated: Christ." ( John.1:41)
(Jesus:) "He brought him to Jesus. Having looked upon him, Jesus said: You are Simon the son of Jonas, you shall be called Cephas, which is translated: Rock." ( John.1:42)

It would seem that the Gospel writers are being careful to preserve Aramaic when it occurs. The fact that they would do so doesn't make much sense if Jesus normally spoke in Aramaic. In fact, if Jesus routinely preached and spoke in Aramaic, why didn't the Gospel writers translate everything into Greek? The fact that the Gospel writers went to some trouble to carefully record a few instances of Aramaic—with Greek translations—would suggest that Aramaic was the exception and not the rule.

None of these are hard proofs; I don't believe hard proof is possible based on the paucity of the available evidence; but I think the preponderance of evidence is that Jesus preached in Greek.