Use of "Mac" or "son"

[emolas]

I'm sure someone here is an expert on it and can give a more accurate answer but, as I understand it:

Way back before surnames they would frequently use your profession to identify two people with the same name. If there were two Gregors in the village, one of them would be Gregor the smith and the other would be Gregor the miller. If Gregor Miller had a son, he wouldn't name him "Bob, son of a miller", he would name him "Bob, son of Gregor" or Bob MacGregor.

Also, I'm sure there were a few sons who weren't too proud of their fathers and so chose not to be known as "son of...".

That's my take on the matter.

[McClef]

You also have to remember that the usage would have been more in the Highlands where Gaelic was more commonly spoken.

The lowlanders would not have used Mac as much and many surnames originated with being linked to the trade being practiced - Miller being one example.

Some surnames had son attached to them as a variant but not all did.

And some ended up with both English and Gaelic variants such as Robertson (Donnachaidh/McDonnachaidh).

Here in Wales certain surnames attracted Ap (son of in Welsh) and some did not and some mutated so that Ap Robert became Probert for example.

But the tradition with very common names such as Jones or Evans was to describe the person by their trade such as "Jones the Milk" and "Evans the Coal."

It's a rich area of study.