The phrase ‘ipse dixit’ means ‘he himself said it.’ The term is used to describe a type of argument in which the person presents one or more assertions, as if each statement were certainly true, but without any support. This is a common type of false argument used today.
Among Catholics, this argument often takes the form of a series of assertions about what the Church does and does not teach: “The Church teaches this; the Church does not teach that. Holy Mother Church does not consider that to be true, but only this.” Now if the Church does teach what is being asserted, and if this is (or should be) common knowledge among Catholics, then it is fine to make such assertions. However, even when true, an unsupported statement is not a philosophical or theological argument. Although it is sometimes useful to make a series of assertions about what the Church teaches, it is more useful if each assertion is supported with a theological argument, including perhaps some quotes from Saints, quotes from Sacred Scripture, or quotes from magisterial documents.
The problem is that many Catholics are ignorant as to what the Church actually teaches. And yet they take it upon themselves to teach and correct others, based on their own ignorance and misunderstanding. This happens quite often online. And when the person making these baseless assertions is anonymous, the situation is even more ridiculous.
“This is true. Believe it because I say that it is true.”
But who are you?
“I wish to remain anonymous.”
But you are making a claim about a grave matter of faith or morals. Why should anyone believe the unsupported claims of an anonymous person? “Because other anonymous persons agree with me.”
They hide behind anonymity. They never accept correction. No opposing theological argument is worthy of consideration. All magisterial quotes, contradicting their position, are dismissed as a misinterpretation. They present no real theological argument of their own.
And yet, the ‘ipse dixit’ argument is surprisingly effective, when it tells people what they want to hear.