“The first sentence of the actual Life of Alexander lives up to Plutarch's warning words. 'Alexander's descent, as a Heraclid on his father's side from Caranus, and as an Aeacid on his mother's side from Neoptolemus, is one of the matters which have been completely trusted.' While the Heraclid and Aeacid descent went unquestioned by ancient writers, the citation of Caranus as the founding father in Macedonia and so analogous to Neoptolemus in Molossia was not only controversial but must have been known to be controversial by Plutarch. For he was conversant with the histories of Herodotus and Thucydides. which had looked to Perdiccas as the founding father in Macedonia. Caranus was inserted as a forerunner of Perdiccas in Macedonia only at the turn of the fifth century: he appeared as such in the works of fourth-century writers, such as Marsyas the Macedonian historian (FGrH 135/6 i- 14) who on my analysis was used by Pompeius Trogus (Prologue 7 'origines Macedonicae regesque a conditorc gentis Carano'). Thus the dogmatic statement of Plutarch, that Caranus was the forerunner, should have been qualified, if he had been writing scientific history. But because the statement conveyed a belief which Alexander certainly held in his lifetime it was justified in the eyes of a biographer and in the eyes of those who were more concerned with biographical background than with historical facts. If Plutarch had been challenged, he would no doubt have claimed that his belief was based on his own wide reading of authors who had studied the origins of Macedonia and provided 'completely trusted' data.”

"Sources for Alexander the Great: An Analysis of Plutarch's 'Life' and Arrian's 'Anabasis Alexandrou'", p.5, Cambridge Classical Studies