For ancient dream interpreters, the most important thing to know about a given dream was the class, status and character of the person that dreamed it. A basic issue might be whether the person in question was a big eater, in which case a disturbing dream was more likely to stem from indigestion than from divine premonition. If a dream happened to be straightforwardly about someone’s daily business or a matter to which they’d recently been giving a lot of thought, then it was probably only a continuation of those processes and, again, of no predictive value.
Supposing you did go to bed with an empty stomach and a clear head, though, it still mattered whether you were a carpenter or a king. Artemidorus of Daldis, the most famous of ancient dream interpreters, demonstrates this using an example taken from Homer. If anyone else had dreamed the dream that Agamemnon did in book 2 of the Iliad, no one would have paid it any attention, and they would have been right to disregard it: a dream like that, affecting the whole Greek army, could only have been sent to its leader. If, ironically, the dream turns out to be a trick, it’s at least a trick sent by the gods, so still proves Artemidorus’ point that only important people get important dreams.
This is so to speak an empire-friendly approach to dream interpretation. Writing sometime during the early second century CE, indeed, Artemidorus cannot but be attentive to the hazards of writing about fortune-telling in a Roman imperium whose rulers were increasingly paranoid about the dangers of the oracular arts, imagined and real. Some emperors are said to have believed in various forms of what we would call magic, meaning I suppose that they also thought magic practitioners could do them harm. Even non-believers were wary, however, of the power a prediction couched in terms of astrology, oneiromancy or whatever had over the substantial portion of the Roman populace (and elites, too) that took those arts seriously. A horoscope indicating that the emperor was soon to be replaced could certainly help to bring about what it predicted.
This put fortune-tellers and their clients in a delicate position and sometimes in real danger. Astrologers and their ilk were more than once expelled from the city of Rome, though not threatened with anything more violent until the fourth century. Earlier than that, in the first and second centuries CE, plenty of Roman aristocrats got put to death because they had allegedly ordered a horoscope cast for the emperor. In individual cases, one can hardly judge whether the charge was true or a pretext; that it was so often leveled, however, suggests this was the kind of crime for which other senators might accept that one of their own had to be put to death.
The fortune-tellers themselves responded to such threats in various ways. Alexander of Abonoteichos, for instance, cannily held onto questions sent by Roman senators to the oracle he managed: they were excellent instruments of blackmail, since in many cases their content, had it been known to the emperor, might have meant death for the questioner. Artemidorus’ approach, like that of ancient handbook-writers in most predictive fields, is more evasive. By establishing at the outset that only the emperor can dream dreams of relevance to the empire as a whole (and dreams about the emperor dying or being deposed would certainly count), Artemidorus seeks to neutralize the threat posed by his art – and likewise, perhaps, to give clients who sought interpretations for such dreams a ready-made excuse should news of this get back to the emperor.
An interesting exception to the rule comes at the end of the section in which Artemidorus introduces it: οὐ γὰρ ἑνὸς ἰδόντος ἀπέβη ποτὲ ἰδιώτου ὄνειρος εἰς τὸ κοινόν, ἀλλὰ πολλῶν κατὰ τὸ αὐτό, ὧν οἱ μὲν δημοσίᾳ ἀναγορεύουσιν οἱ δὲ ἰδίᾳ ἕκαστος. καὶ γίνεται οὐκ ἰδιώτης ὁ ἰδὼν ἀλλὰ καὶ στρατηγοῦ καὶ ἄρχοντος οὐδὲν ἥττων δῆμος· ἀγαθοῦ μὲν γὰρ ἐσομένου κοινοῦ πόλει μυρίους ἄν τις ακούσαι λεγομένους ὀνείρους, οἳ σημαίνουσι τὸ μέλλον ἄλλος ἀλλοίᾳ καὶ διαφόρῳ ὄψει.
“A private citizen’s dream never came true for the community just because one private citizen saw it, but only when many people foresaw the same thing, of whom some interpret it with respect to the people and others with respect to themselves. And [in that case] it is not a private citizen who sees it, but a demos, which is no less than a general or an archon. If something good were going to happen to the city as a whole, then one would hear thousands of people recounting dreams, which each signify the thing to come in a different manner and with a different vision.”
The demos is no less significant a figure than Agamemnon or the emperor or whoever. Its dreams, however, are infinitely harder to interpret, because, like the demos itself, they are many. It’s not just that lots of people need to be dreaming the same thing at once: unless you’re a skilled interpreter, you might not even be able to tell that lots of people are dreaming the same thing at once, since they’ll be receiving the same message via different opseis or visual presentations. That makes the dream interpreter a figure of central political importance, or, conversely, it means that a politician needs to have all the skills of a dream interpreter. After all, a real politician isn’t interested only in what the demos wants, but in what’s going to happen to it.