Okay, this is long, but I hope you’ll find it interesting.
Scottish names in the past were different in many ways from modern names. There was also a difference between Highland and Lowland naming conventions, just as there were differences in language, culture, and social organisation. In some ways the Highlands and Lowlands were more like different countries than parts of the same country.
Lowland names and land ownership
The Lowlands were simpler than the Highlands in terms of naming. The Anglo-Saxon-Norman culture and the English language (or a dialect of it) predominated, and names were mostly the same as in England.
The only real difference was in the use of estate names. If someone was a landowner, he would go by the name of his estate.
e.g. John Graham of Claverhouse meant that John Graham owned an estate called Claverhouse. He would normally be referred to and addressed as ‘Claverhouse’.
“I spoke to Claverhouse.”
“Claverhouse went here and did that.”
“Claverhouse, would you like a drink?”
The ‘of’ epithet indicated a land-owner, a gentleman, member of the upper classes.
But it was different from both the German ‘von’ and the Dutch ‘van’, in that it was always attached to only one individual, and indicated actual, current ownship of an estate. So if Graham of Claverhouse sold his estate and bought another one, he would be ‘of’ somewhere else, and the current owner would be ‘Claverhouse’. That worked in practice because land ownership was generally very stable and usually passed down by inheritance.
This convention was pretty much universal in the Lowlands, and historical names of landowners are always given as ‘first-name surname of somewhere’. e.g. “James Boswell of Auchinleck” (pronounced Affleck).
This often applied to clan chiefs in the Highlands as well. So, for example, Sir Ewan Cameron of Lochiel was chief of the Cameron clan, and was usually called only ‘Lochiel’. But since clan chieftainships were inherited along with property, ‘Lochiel’ for many generations meant whoever was the current chief of the Camerons (and still does today) - even after the actual seat of the Cameron chiefs became Achnacarry Castle. And ‘Cluny’ is the chief of the Macphersons. So also Glengarry, Keppoch, Glengyle, etc. But it varied by clan, and sometimes over time.
Next we turn to the ‘clan system’ up to the mid-18th century.
People today generally don’t realise just how ‘tribal’ life was in the Highlands, and how little it had changed since very ancient times. ‘Clan’ is simply the Galic word for ‘tribe’. In English ‘clan’ has come to mean something smaller than a ‘tribe’, but it’s useful to think of clans in terms of tribes, really no different from Mohawks, Apaches, Zulus, Xhosas, etc. except in size.
Names like MacDonald, Campbell, McLeod, Macintosh, Cameron, etc. were originally the names of the tribes / clans, like Sioux, Blackfoot, etc. There were frequent feuds, battles, and raids between the clans.
The clan chief had absolute authority of life and death over the members of the clan, and the right to call on members of the clan for military and other service. Celtic tribes or clans also had an inherited aristocracy. A duine-uasal or duniewassal (normally translated into English as ‘gentleman’) was of a far higher status than an ordinary clansman.
Land ownership among the clans was complicated, with a semi-feudal system of ‘tacksmen’ below the chiefs. To simplify a messy, inconsistent sytem varying by region and over time, land belonged in general to the clan as a whole rather than to individuals, though there was a system of rents, service, and inheritance.
The name MacDonald meant that you belonged to Clan MacDonald, with a close reciprocal relationship within that social structure, and it meant that the chief had authority over you.
The larger clans had sub-clans, called ‘septs’. We normally talk of ‘the MacDonalds of Glencoe’, but we could just as well call them ‘the MacIains of Glencoe’ (that’s a capital i in there, not a small L). MacIain was a sept of MacDonald, living in the valley of Glencoe. So the MacIains were MacDonalds. An individual could call himself either ‘Colin MacDonald’ or ‘Colin MacIain’, depending on whether he was emphasising the larger or the smaller grouping he belonged to. His name was was both MacDonald and MacIain.
(To put it another way, all the MacIains were MacDonalds, but only a few of the MacDonalds were MacIains. Similarly, all the MacCrimmons were MacLeods, but only a subset of MacLeods were MacCrimmons. MacCrimmon was sept of Clan MacLeod. There are hundreds more examples.)
The chief of the MacIains was simply referred to as ‘MacIain’ with no first name. Every chief of the MacIains was ‘MacIain’, whatever his personal name. But he was not called simply ‘MacDonald’, because that would indicate chieftainship of the whole wider clan. He was, of course, a MacDonald.
Certain lowlanders (a small proportion) were considered to be ‘clans’ too, even though they were English speaking and of Saxon-Norman heritage and culture. (In Gaelic, ‘Sassenach’ = ‘Saxon race’). They owed a feudal allegiance to a lord, indicated by their name.
The Duke of Montrose was the lord of the Grahams. That meant that if your name was Graham (like John Graham of Claverhouse), then the Duke of Montrose had a right to call on you for military service, and you had a right to go to him with a problem or grievance, and he had some kind of obligation to do something about it. A patron-client relationship in other words, something like a Mafia Don (but entirely legal, open, and above board). This survived far into the 18th century and even the early 19th century.
Similarly with the Drummonds and the Earl of Perth, the Murrays and the Duke of Atholl, the Gordons and the Marquess of Huntly, the Campbells and the Duke of Argyll (the Campbells were originally a Highland clan, but became integrated into Lowland culture), and others.
If, say, a Graham changed his allegiance and became a retainer of the Earl of Peth, he would change his name to Drummond to indicate that. And if your name was Drummond, the Earl of Perth had some kind of claim on you - whether you liked it or not.
That was why, when the name MacGregor was banned by King James VI after Battle of Glen Fruin in 1603, it was considered to be a harsh and serious punishment. Today it would be meaningless to outlaw a surname, but then it had serious and practical consequences. The MacGregors unofficially kept their name and clan allegiance, but officially they were forced to take other names. That meant they were officially part of other Highland or Lowland clans, and therefore under the authority of their chiefs.
The famous Rob Roy MacGregor had the official name ‘Robert Campbell of Inversnaid’, and later ‘Robert Campbell of Craigroystan’ when the property he owned changed. (‘Roy’ means that he had red hair.) His official name had its positive side too, because after he was outlawed, the Duke of Argyll (the chief of the Campbells) tacitly protected him and allowed him to live on Campbell land.
So that’s the general overview. I hope it all makes sense!