Few will need to be told that the "Mac" in Scottish names, and Irish names for that matter, means "son". Unfortunately, however, a good deal of confusion exists as to the correct spelling of such names. Sometimes the prefix is contracted to "Mc", while the following word is sometimes spelled with a capital and sometimes with a small letter. There are "McDonald," "MacDonald," and "Macdonald," and so with many other Scottish names.
It may happen that there is more than one recognized spelling of a clan name, though it is desirable that only one spelling be accepted, as such differences in spelling have given rise to the introduction of entirely new names. It is also desirable, of course, that the form of spelling should be that which best preserves the distinctive character of the name. The form "Mc" is an abbreviation and should never be used. It is scarcely worth while spoiling a word for the sake of a single letter. There are some who think that the form "Mc" is Irish while "Mac" is Scottish. While it is true that "Mc" is more commonly used in Irish names, yet this form is neither Irish nor Scottish, the word "son" being exactly the same in both Irish and Scottish Gaelic. The use of the form "Mac" appears to be much commoner in Ireland now than formerly, a result, no doubt, of the new Gaelic movement in that country.
As for the word following "Mac", the rule generally given is that when it is a proper name it should be spelled with a capital letter, otherwise a small letter should be used, as MacDonald, MacDougall. According to this rule, such names as MacGregor, MacKenzie, should be spelled with a capital letter, as Donald, Dougall, Gregor and Kenzie (used for Kennith), are proper names, while names like MacIntosh and MacPherson would be spelled with a small letter. The rule appears logical enough, and certainly no one can say that a MacPherson, for instance, who spells his or her name "Macpherson" is wrong. At the same time it is very desirable that there should be uniformity in spelling, and therefore it is best, if the practice can be justified, to use the capital letter even when the word following the "Mac" is not a proper name.