Dear Tryphon:

Your friend is wrong, of course. Since he is arguing this I presume he his Eastern Orthodox. The Eastern Orthodox think they are the original Church and the the Western Church split from them. This is impossible as Peter cannot split from Peter. Christ built his Church upon the Magisterial Chair of Peter. In the Old Covenant it was the Chair of Moses (Matt 23:2). In the New Covenant, it is the Chair of Peter (Matt 16:18-19). Verse 19 was a quotation of Isaiah 22:22 (v. 21-23), which is about the succession of the office of Prime Minister (Pope).

This is the reason I converted from a Baptist preacher to a Catholic—that along with John 6 about the Eucharist, proves without any doubt, from the Bible alone, that Jesus continued the tradition that had been in place for 1000s of years, the tradition of a chair of authority for his people, a prime minister (Pope), and that Peter was the first Pope, the Rock to which the Church of the New Covenant was built upon.

Thus, in the dispute over the Filioque, the Magisterium of the Catholic Church under the pope had the authority to interpret this doctrinal issue. When the Eastern Orthodox refused God's legitimate authority, they, and the the West, went into schism. 

These are the Biblical and historical facts regardless of what the Eastern Orthodox say.

This is an argument that generally devolves quickly into an unproductive argument. St. Paul tells us to stay away from unproductive arguments, thus, because of that, and because of my own experience, this one may best to walk away. The argument normally serves only discord and not truth.

As for the Filioque the argument is this:

The Eastern Orthodox interpret the Nicene Creed as saying: in the Greek text of the Nicene Creed as originally formulated at the First Council of Constantinople, which says only that the Holy Spirit proceeds "from the Father".

The Western Church (Catholic Church) interpret the Nicene Creed as saying: in the Latin text of the Nicene Creed speaks of the Holy Spirit as proceeding "from the Father and the Son".

In the Greek, the difference between these two interpretations is found in the Greek letter, "iota" in the word Homoousios meaning "same substance" or "same essence" saying that is one essence with the Father."

The competing term at the First Ecumenical Council was homoiousios meaning "similar essence"; it was favored by the Arians. Because of how close these two words are in the Greek, it has been said that there was only "one iota" of difference between them.

Because of how close these two words are, it is the origin of the phrase today, "not an iota of difference."

Since it is the Pope and the Magisterium of the Catholic Church that has the sole authority to declare and interpret doctrine, it is the interpretation of the Catholic Church that trumps the interpretation of the Eastern Orthodox. This is not an opinion, but a fact as the Prime Ministry of God is upon the Chair of Peter.

A fuller discussion is found at Catholic Answers and in the Catholic Encyclopedia.

God Bless,
Bro. Ignatius Mary