A thought I hope might be helpful in cases like these.

I rarely argue with Catholics specifically about Mary or Communion or the Papacy, because these issues are all secondary to a grossly insufficient view of the Word of God. Arguing just means hurt feelings. What is needed is generally the Gospel, and prayer. That the person in question would be saved, or, if he or she already is, then for spiritual growth, such that they would understand that the Word of God is infinitely superior to the word of sinful man. Then, but only then, will they likely be open to sound Biblical teaching.

It is very much the same thing IMO when dealing with Arminians or semi-Pelagians. Like Catholics, they trust in a "gospel" that is subtlely, and hence dangerously, inadequate. Arguing about the Solas or TULIP or even the attributes of God rarely works. But the Gospel, and prayer, might. As for anyone else, these are means by which God saves and then grows His children. And like Catholics, Arminians must learn that the Word of God is infinitely superior to the word of man. But I think they can only learn this from the Holy Spirit, and not from arguments about things that, though important, are secondary to knowing Him as He truly Is.

Once a person is committed to knowing, loving, and serving God, as He really and truly Is (not the false "gods" of Rome or Pelagius), the rest should follow naturally. A person so committed will be willing to learn. It will then be a joy, and not a struggle, to introduce them to those important truths that we in the Biblical, Protestant, and Reformed tradition hold dear.

Aspiring student of Christ