Milton’s prose work An Apology for Smectymnuus (1642) contains autobiographical details that shed light on the philosophy that underlies Comus. The tract argues for reform in the structure of the Church of England while also refuting charges of immorality made against Milton by describing his youthful reading, his education at Cambridge, and his ideals and purpose as a man and a poet. 

In the Apology, Milton writes with feeling of his dedication to chastity and virtue. He suggests that if a poet wishes to write well of honorable things, he ought to be a “true poem” himself, “a composition, and patterne of the best and honourablest things; not presuming to sing high praises of heroick men, or famous Cities, unlesse he have in himselfe the experience and the practice of all that which is praise-worthy.” (Milton, John. An Apology against a Pamphlet). He tells of how he read fables and romances about the deeds of great knights, every one of whom took an oath to defend with his life the honor and chastity of “virgin or matron.” From that reading he learned “what a noble virtue chastity sure must be” (An Apology). If later he found in the story any example of a knight having broken his oath, he judged it to be the fault of the poet rather than the knight. He also decided that: 

[E]very free and gentle spirit without that oath ought to be borne a Knight, nor needed to expect the guilt spurre, or the laying of a sword upon his shoulder to stirre him up both by his counsell, and his arme to secure and protect the weaknesse of any attempted chastity (An Apology).

Whatever Milton read, he states, even books that led others to pursue a dissolute life, produced in him only “stedfast observation of that vertue which abhorres the society of Bordello’s” (An Apology). For Milton, moral character and artistic creation/consumption are thus inherently intertwined, even in works less overtly ideological than Comus.

From there, Milton was led to study the philosophy of Plato and his contemporary Xenophon. From those philosophers, he learned much: 

Where if I should tell ye what I learnt, of chastity and love, I meane that which is truly so, whose charming cup is only vertue which she bears in her hand to those who are worthy. The rest are cheated with a thick intoxicating potion which a certaine Sorceresse the abuser of loves name carries about; and how the first and chiefest office of love, begins and ends in the soule, producing those happy twins of her divine generation knowledge and vertue (An Apology).

The passage suggests what Milton had in mind when he wrote Comus. The “certaine sorceresse” is Circe, and the “intoxicating potion” is what her son, Comus, tries to get the Lady to imbibe. The “office of love” is an allusion to the myth of Cupid and Psyche (mentioned in Comus), as seen through a Platonic-Christian lens. Overall, Milton’s discussion exemplifies the synthesis of classical myth and Christian ideology that animates Comus. 

Milton also declared, based on his reading in Christian scriptures, especially Paul’s first letter to the Corinthians, that chastity was equally a male virtue as well as a female one. Indeed, unchastity in a man: 

[W]ho is both the image and glory of God, it must, though commonly not so thought, be much more deflouring and dishonourable. In that he sins both against his owne body which is the perfeter sex, and his own glory which is in the woman, and that which is worst, against the image and glory of God which is in himself (An Apology).

Though Milton takes for granted women’s inferiority, his challenge to the double standard surrounding sex underscores the importance he placed on chastity. In a similar vein, Milton notes the passage in the Book of Revelation (14.3-4) about the redeemed souls that sing before the throne of the Lamb of God. They are the only ones who can learn and understand those, in Milton’s phrase, “celestiall songs”; those who were “defil’d with women” cannot (An Apology). This, Milton states, “doubtlesse meanes fornication: For mariage must not be call’d a defilement” (An Apology). Such remarks demonstrate the centrality of Comus’s themes, including Virtue Versus Vice and The Invincible Nature of Chastity, to Milton’s broader philosophy.