McCarthy or MacCarthy?
There are a number of different variations on the name McCarthy. This is because historically written language was not as formalised as it is today and therefore the exact spelling of one's name was not considered particularly important. Names instead were recorded as they sounded, and in many cases a name could change with every time it was listed.
One notable example is the case of the Bard himself. During William Shakespeare's lifetime there is no recorded, consistent spelling of his name, leading to an ongoing debate as to how we ought to spell it now. Even the spelling in his own signatures vary significantly, written as 'Shakspeare', 'Shaksper', 'Shakspere' and 'Shakspe'.
There are many derivations of the name McCarthy, including, MacCarthy, MacCarthaigh, McArthy and McArty. Although the spelling varies, each of these names shares a common origin. So whether you're a McCarthy or a MacCarthy, you're part of the clan.