Question: A preacher on the radio claims that in the early Church, Christians believed that Mary had children in addition to Jesus, and that he has read the statements of several Popes to this effect. He claims that it is up to Catholics to prove him wrong. How can we do that?
Answer: Proving that early Christians accepted the perpetual virginity of the Blessed Mother isn't all that difficult. There are writings by some of the Fathers of the Church -- men generally recognized as authoritative by all Christians, and recognized as representative by most historians -- there are also some pronouncements by early ecumenical councils. But as far as proving him incorrect about the teachings of a specific papal pronouncements, the burden of proof is on him to produce them
It is relatively easy to prove that something exists or took place at some time. What is much more difficult, and perhaps impossible, is to prove that something did not exist or happen.
Most reasonable people are willing to agree that an event took place if they can be shown a few unbiased and pertinent references or other forms of evidence. For example, one might "prove" that a particular military battle took place by the records of the two armies, hospital charts, grave stones, and church burial records. Not all "evidence" is valid and some is more trustworthy than others. There might be some discussion as to why one or more record might be false or deceptive or created by someone who didn't actually know the situation, but reasonable people can usually agree as to how evidence is to be evaluated. Someone less critical might simply accept the word of a few history books or encyclopedia articles.
The point is that we can "prove" something existed by gathering evidence acceptable to all parties in a discussion. But not finding evidence doesn't necessarily mean that something didn't happen. We might be looking in the wrong place: Maybe our battle took place in Springfield, Massachusetts and not in Springfield, Illinois; during the Revolutionary War and not the Civil War; maybe the physics and botany text books of the period didn't think it was important. The "battle" may have been no more than a "fight," not recorded anywhere. If there were records, they may no longer exist. And, even if one party has looked in every conceivable place and found no evidence, he really has nothing tangible to show the other party to the discussion. "Proving" absolutely that something never happened or does not exist would take an infinite search conducted jointly by both parties!
For this reason, the "burden of proof" normally rests on the party who claims that something exists or happened (for he should have some evidence -- some reason -- for his belief). The pparty who disagrees can reasonably say, "show me." The preacher who claims to have read papal decrees on devotion to the Blessed Mother can reasonably be asked to produce his evidence.
Scholarly and responsible writers usually document their major claims without
being asked. Their writings include footnotes or references within parentheses.
Readers ought to be suspicious of writers who make surprising claims and no
attempt to document them. But note that footnotes don't prove anything. They
simply state where a piece of information was found. That way, an interested
reader can consult the writer's sources for himself, both to be assured that the
source actually exists, and to see if he agrees with the writer's assessment of
it. Prudent readers occasionally check the footnotes, even of writers whom they
trust and with whom they generally agree, for "evidence" isn't always
what it is claimed to be, translations aren't always accurate, and sometimes
people make statements having no basis in reality. Witness your man on the
Considerations on Evaluating Written Evidence
* Is the source primary or secondary -- does the author have first or second
hand knowledge of the event -- or is he commenting on the writings of those that
do, or on the writings of other commentators?
Considerations on Evaluating Commentary on Evidence
* Is the presentation in the document logical, or does it rely on emotional
and illogical arguments? Be familiar with inductive fallacies such as the ad
hominem, post hoc, "begging the question,"etc.