Such evidence as there is for the date of the composition of the dialogue points to a period not earlier than 385 B.C., but the time of the party of which it purports to give an account is securely fixed in 416 B.C. by its connexion with the dramatic triumph of the host, Agathon. That the conversation which takes place at it is fictitious cannot seriously be doubted, but Plato has been at unusual pains to impart to the whole scene a deceptive air of authority. The direct speakers are only two in number, Apollodorus and an unnamed friend, to whom among others Apollodorus reports at second-hand and many years after the event, though before the death of Socrates in 399 B.C., an account which he has had of the party from a member of Socrates' circle called Aristodemus, who was actually present at it. Since one of the main objects of the dialogue is to praise Socrates, it is clear that Socrates himself cannot be the narrator, but that in itself hardly explains the use of such curiously elaborate machinery. The effect is much the same as that given by Boswell when he reports some incident in Johnson's life which took place before their meeting and just as Boswell often states that he has confirmed what he tells us by direct application to Johnson, so Apollodorus asserts that he has questioned Socrates on some points in Aristodemus' account. Plato's motive in all this seems to be to heighten the plausibility of his historical fiction by appealing to the authority of apparently unimpeachable witnesses; both Apollodorus and Aristodemus are historical persons, whom we know from other sources to have been fanatical admirers of Socrates.
So too, the guests named as having been present at Agathon's party are real people, and the whole atmosphere is such as we may readily believe to have existed among the upper classes at Athens in 416 B.C. when nothing had yet occurred to impair the mood of carefree and almost insolent superiority which found its supreme expression in Alcibiades. A year later his ambition was to lead his city into the disastrous adventure of the Sicilian expedition, which began the long death-agony of the Athenian Empire and involved him in dishonour and ruin; but no hint of this is allowed to intrude, and the picture of Alcibiades in the last scene of the dialogue, brilliant, charming, and completely shameless, for all that it must be an imaginative reconstruction, is as valuable evidence for his character and for the nature of the spell which he cast over his contemporaries as the substance of what he says is for the character of Socrates.
At this point a brief account of the structure of the dialogue may be helpful. Aristodemus meets Socrates on his way to dine with Agathon, a tragic poet, who is celebrating his recent success in the dramatic competition. Socrates takes Aristodemus with him, but does not arrive till the meal is half over. Eryximachus, a doctor, whose fussy officiousness is portrayed with admirable humour, then proposes that instead of the usual entertainment by flute-girls the company shall amuse itself with talk, and that this shall take the form of a speech from each member of the company in praise of love. His proposal is adopted, and the main section of the dialogue consists of speeches delivered by Phaedrus, who is said to be the real author of the idea, Pausanias, who according to Xenophon was notorious for his devotion to Agathon, Eryximachus himself, Aristophanes, the great comic poet, Agathon, and Socrates, with interludes between them. At the conclusion of Socrates' speech a commotion is heard outside, and Alcibiades enters with some drunken companions and is warmly welcomed. The party becomes much less decorous; Alcibiades takes the lead, and, when he is invited to contribute to the original scheme, declares that the only subject on which he is willing to make a laudatory speech is Socrates. He proceeds to give at some length a sketch of the character of Socrates and of his own relations with him. Finally a fresh party of revellers bursts into the house; all restraint is cast aside; some of the guests become incapable, others go home, and Aristodemus falls asleep. When he awakes towards morning he finds only Agathon, Aristophanes, and Socrates still drinking and talking; shortly afterwards the two former succumb, and Socrates leaves as fresh and sober as when he arrived, with Aristodemus still in attendance.