The Q source is a theory concerning the source of the four Gospels of Matthew, Mark, and Luke. Matthew, Mark, and Luke have many similarities, so many say they must have copied from one another or from another source. The name that has been given to this possible other source is the “Q source.”
The theory concerning the Q source is this:
It is certainly possible that the Q hypothesis, as it is stated above, is legitimate. However, there are several things to consider regarding the Q source:
There are other theories that can help explain the similarities between the Gospels of Matthew, Mark and Luke that do not involve this supposed source.
For example, it is very possible that Matthew, Mark, and Luke copied from each other without the use of another source.
Alternatively, there may have already been several writings that had been circulating, and Matthew, Mark, and Luke utilized these other writings.
In any case, there can be a reasonable explanation for why the Gospels of Matthew, Mark, and Luke have so many similarities between them without compromising the doctrine of biblical inerrancy.