And knew her not This passage afforded the pretext for great disturbances, which were introduced into the Church, at a former period, by Helvidius. The inference he drew from it was, that Mary remained a virgin no longer than till her first birth, and that afterwards she had other children by her husband. Jerome, on the other hand, earnestly and copiously defended Mary’s perpetual virginity. Let us rest satisfied with this, that no just and well-grounded inference can be drawn from these words of the Evangelist, as to what took place after the birth of Christ. He is called first-born; but it is for the sole purpose of informing us that he was born of a virgin. [FN: French has “Il est nomme Premier nay, mais non pour autre raison, sinon afin que nous sachions qu'il est nay d'une mere vierge, et qui jamais n'avoit eu enfant;” — “he is called First-born, but for no other reason than that we may know that he was born of a pure virgin, and who never had had a child.”] It is said that Joseph knew her not till she had brought forth her first-born son: but this is limited to that very time. What took place afterwards, the historian does not inform us. Such is well known to have been the practice of the inspired writers. Certainly, no man will ever raise a question on this subject, except from curiosity; and no man will obstinately keep up the argument, except from an extreme fondness for disputation.- John Calvin, Commentary on Matthew, Mark, and Luke at Matthew 18:25
Some Roman Catholics and Eastern Orthodox folks have taken these comments from John Calvin to suggest that Calvin was endorsing the dogma of the perpetual virginity. This is a mistaken idea. While Calvin does appear to accept Jerome's position of perpetual virginity (absence of sexual union virginity, not also in partu virginity) over Helvidius' more Scriptural position of limited virginity (virginity until Christ was born), Calvin does not attempt to make this a dogmatic position. He views the issue as one that is of limited interest, mostly of interest to those who have nothing better to think about. That's partly because Calvin lived in an age before Rome had defined the perpetual virginity as a dogma. Had he lived in that day, he might have spent more time considering the matter carefully and been less quick to dismiss Helvidius' arguments. Of course, we cannot be sure, but he does seem to reject many of the interpretations upon which Roman Apologists depend today.
It should be noted as well that at Luke 1:34, Calvin comments:
The conjecture which some have drawn from these words, that she had formed a vow of perpetual virginity, is unfounded and altogether absurd. She would, in that case, have committed treachery by allowing herself to be united to a husband, and would have poured contempt on the holy covenant of marriage; which could not have been done without mockery of God. Although the Papists have exercised barbarous tyranny on this subject, yet they have never proceeded so far as to allow the wife to form a vow of continence at her own pleasure. Besides, it is an idle and unfounded supposition that a monastic life existed among the Jews.- John Calvin, Commentary on Matthew, Mark, and Luke at Luke 1:34
This commentary shows us that if Calvin had been considering the issue in more depth, would not have adopted at least some of the arguments that Roman Catholics present. Specifically, Calvin properly rejected as absurd the idea that Mary's comment "I know not a man" is suggestive of any vow of perpetual virginity.
Furthermore, Calvin rejected the excessive praise of Mary that the Roman Catholics of his day employed:
Woman, what have I to do with thee? Why does Christ repel her so rashly? I reply, though she was not moved by ambition, nor by any carnal affection, still she did wrong in going beyond her proper bounds. Her anxiety about the inconvenience endured by others, and her desire to have it in some way mitigated, proceeded from humanity, and ought to be regarded as a virtue; but still, by putting herself forward, she might obscure the glory of Christ. Though it ought also to be observed, that what Christ spoke was not so much for her sake as for the sake of others. Her modesty and piety were too great, to need so severe a chastisement. Besides, she did not knowingly and willingly offend; but Christ only meets the danger, that no improper use may be made of what his mother had said, as if it were in obedience to her command that he afterwards performed the miracle.- John Calvin, Commentary on John, at John 2:4
The Greek words (Τί ἐμοὶ καὶ σοὶ) literally mean, What to me and to thee? But the Greek phraseology is of the same import with the Latin — Quid tibi mecum? (what hast thou to do with me?) The old translator led many people into a mistake, by supposing Christ to have asserted, that it was no concern of his, or of his mother’s, if the wine fell short. But from the second clause we may easily conclude how far removed this is from Christ’s meaning; for he takes upon himself this concern, and declares that it belongs to him to do so, when he adds, my hour is not yet come. Both ought to be joined together — that Christ understands what it is necessary for him to do, and yet that he will not act in this matter at his mother’s suggestion.
It is a remarkable passage certainly; for why does he absolutely refuse to his mother what he freely granted afterwards, on so many occasions, to all sorts of persons? Again, why is he not satisfied with a bare refusal? and why does he reduce her to the ordinary rank of women, and not even deign to call her mother? This saying of Christ openly and manifestly warns men to beware lest, by too superstitiously elevating the honor of the name of mother in the Virgin Mary, they transfer to her what belongs exclusively to God. Christ, therefore, addresses his mother in this manner, in order to lay down a perpetual and general instruction to all ages, that his divine glory must not be obscured by excessive honor paid to his mother.
This passage tends to show that while Calvin had a high regard for Mary, he was cautious about asserting overly high regard for her.
While we are on the subject, let us consider the fact that (for much the same reason as Calvin above) the real Francis Turretin similarly thought that Mary probably remained a virgin for her whole life:
This is not expressly declared in Scripture, but is yet piously believed with human faith from the consent of the ancient church. Thus it is probable that the womb in which our Savior received the auspices of life (whence he entered into this world, as from a temple) was so consecrated and sanctified by so great a guest that she always remained untouched by man; nor did Joseph ever cohabit with her.- Francis Turretin, Institutes of Elenctic Theology, vol. 2, 345-346 (transcription courtesy of the Eastern Orthodox blog Energetic Procession)
Hence Helvidius and the Antidicomarianites (so-called because they were opponents of [antidikoi] Mary)are deservedly rebuked by the fathers for denying that Mary was always a virgin (aei Parthenon). They held that she cohabited with Joseph after delivery; yea, also bore children from him. As Augustine remarks, they rely on the shallowest arguments, i.e., because Christ is called the ‘firstborn’ of Mary (cf. De Haeresibus 56, 84 [PL 42.40, 46]). For as Jerome well remarks, she was so called because no one was begotten before him, not because there was another after him. Hence among lawyers: ‘He is the first whom no one precedes; he is last, whom no one follows.’ The Hebrews were accustomed to call the firstborn also only begotten; Israel is called ‘the first-born of God’ (Ex 4:22), although the only people chosen of God. Thus ‘the firstborn’ is said to be ‘holy unto God’ (Ex 13:2), who first opened the womb, whether others followed or not. Otherwise the firstborn would not have to be redeemed until after another offspring had been procreated (the law shows this to be false because it commands it to be redeemed a month after birth, Num. 18:16).
Not more solidly have they been able to elicit this from the fact that in the New Testament certain ones are called ‘the brothers of Christ.’ It is common in Scripture not only for one’s own and full brothers by nature to be designated by this name, but also blood relatives and cousins (as Abraham and Lot, Jacob and Laban). Thus James and Joses, Simon and Judas are called brothers of Christ (Mt. 13:55) by a relation of blood. For Mary (who is called their mother by Matthew and Mark) is called by John the sister of the Lord’s mother. However what is said in Jn. 7:5 that ‘neither did his brethren believe him’ must be understood of more remote blood relations.
Nor is it derived better from this-that Joseph is said ‘not to have known Mary till she had brought forth her firstborn son’ (Mt. 1:25). The particles ‘till” and ‘even unto’ are often referred only to the past, not to the future (i.e., they so connote the preceding time, concerning which there might be a doubt or which it was of the highest importance to know, as not to have a reference to the future-cf. Gen 28:15; Pss 122:2; 110:1; Mt.28:20, etc.). Thus is shown what was done by Joseph before the nativity of Christ (to wit, that he abstained form her); but it does not imply that he lived with her in any other way postpartum. When therefore she is said to have been found with child ‘before they came together’ (prin e synelthein autous), preceding copulation is denied, but not subsequent affirmed.
Although copulation had not take place in that marriage, it did not cease to be true and ratified (although unconsummated) for not intercourse, but consent makes marriage. Therefore it was perfect as to form (to wit, undivided conjunction of life and unviolated faith, but not as to end (to wit, the procreation of children, although it was not deficient as to the raising of the offspring.
The same observations apply as noted above. Even more clearly than Calvin, Turretin explains that his belief is merely one of probability, not one having any positive Scriptural warrant. Had Turretin lived in an era when the Perpetual Virginity had been as carefully scrutinized as our day, we have reason to suppose that Turretin would have acceded to the arguments from Scripture. Additionally, Turretin's mistaken belief that this view had "the consent of the ancient church" might have been corrected with additional study of the issue and more careful scrutiny of the patristic evidence.