Are you thinking of becoming a historian? Here is some advice from ancient Greek and Roman writers, on what they thought are the traits and practices of being a good historian, as well as some of the pitfalls of the craft.
1. Herodotus on reporting even stories he does not believe:
I am obligated to recount these traditions, but I am in no way obligated to believe them; and this may be held to apply to my entire work.
2. Thucydides on trusting your sources:
Early times, then, I have discovered to be such, even though it is difficult to trust every single piece of evidence put forward in the traditions about them. For people accept from one another the reports of earlier events in a similarly uncritical spirit, even if the traditions are their own.
3. Polybius on not being biased:
Now in the rest of life one would perhaps not exclude such an attitude: a good man should indeed love his friends and his country, and he should share his friends’ hatreds and alliances. But whenever someone takes up the character appropriate to history, he must forget all such things, and he must speak well of his enemies and adorn them with the greatest praises, when the events demand this, while he must often reproach and reprove severely those closest to him, whenever their failures of conduct deserve such treatment. For just as a living creature deprived of it eyes becomes completely helpless, so when history is deprived of truth what remains is a useless narrative. One must, therefore, not shrink from accusing one’s friends or praising one’s enemies; nor must one hesitate sometimes to find fault with, at other times to praise, the same people: for it is not probable that those who are engaged in political affairs should always succeed or continuously fail. In history, therefore, one must keep some distance from the actors, and instead apply to the deeds themselves the opinions and judgements that are appropriate.
4. Ephorus of Cyme on being an eyewitness:
Ephorus says that if it were possible for historians to be present at all events, this would be much the best form of knowledge.
5. Pliny the Younger, on what type of history should he write:
Nevertheless you can already consider now what era it would be best for me to attempt. Older events which have already been written by others? Here the investigation has already been done, but the comparison of accounts is burdensome. Recent events that have not been treated? Here offences are serious, gratitude slight. For beyond the fact the in the numerous faults of mankind there are more things to blame than to praise, it is also the case you will be called sparing in praise and excessive in criticism even though you are most generous in the former and most restrained in the latter.
6. Josephus on writing beautifully:
It is necessary that a history that reveals matters which, because of their antiquity, are unknown to most people should offer readers a beauty of language in its narration (the kind that arises from the words and their arrangement, and all those things that contribute to artistic adornment), so that their instruction may come with a certain amount of grace and pleasure; but historians must most of all aim at accuracy, preferring nothing to speaking the truth to those who will trust them for deeds that they themselves do not know.
7. Ammianus Marcellinus on avoiding brevity:
Brevity is only to be praised when it cuts short untimely delays but in no way diminishes our understanding of events….In narrating events that are unknown, the one who affects an excessive brevity is on the lookout not for what he might explain more clearly but what he ought to pass over.
8. Lucian on not writing for the present-day:
In general remember this one thing (for I shall say it often): you should write not looking to the present only or so that contemporaries will praise and honour you; instead, aim at all of time, and compose your history with a view to men of the future, and demand from them the reward for your writing, so that it will be said of you, ‘he for his part was a free man and abundantly frank, with no flattery or servility; but truth was in everything he wrote.’ If someone is wise, he would place this above all present-day expectations which are so short-lived.
9. Plutarch on writing a biography:
For we are composing not histories but biographies and it is not always in the most famous actions that one sees virtue or vice revealed, but it is often a little thing or remark or some jest that makes an impression of someone’s character, rather than battles in which countless people die or enormous lines of soldiers or sieges of cities. Just as painters take the likeness from the face and expression of the eyes where character is revealed and pay little attention to the rest of the person, so too we must be allowed to penetrate to the signs of the soul, and through these to make a portrait of each man’s life, yielding to others the great achievements and the struggles.
Let it be written by me, then, up to this point. Events after this may perhaps be the concern of another.
You can read more thoughts about the topic in On Writing History: From Herodotus to Herodian, edited and translated by John Marincola.