I was reading a book by Richard Ibranyi and I came across this condemned proposition from the Council of Constance.

Council of Constance, Session 15, 1415: “Condemned proposition 4: Two natures, divinity and humanity, are one Christ.”(D. 630)

What about this statement is erroneous? If I had been presented this I never would've guessed that this would be a condemned proposition since Christ is fully Human and Divine. Because a Council of the Church condemns it there has to be something erroneous about it.

I think the objectionable part is clear by what's around that phrase in Hus' writing:

"And so Christ is the outward head of every particular church and of the universal church by virtue of his divinity, and he is the inward head of the universal church by virtue of his humanity; and these two natures, divinity and humanity, are one Christ, who is the only head of his bride, the universal church, and this is the totality of the predestinate."

This is from Hus' writing on the Church. Basically, he's saying Christ is head of the church by divinity and humanity and these two natures are one head of the church, Christ. Since he's saying Christ is the only head of the Church, I take it he's saying the Pope is not head of the Church.

https://en.m.wikisource.org/wiki/Page:The_Church,_by_John_Huss.pdf/80

The aspect of Hus's teachings that was objected to most strongly was that the Church on earth consisted solely of those predestined by God for salvation (such is the meaning of the term "predestinate," referred to above). On the other hand, his teaching with regard to the two natures constituting the single person of the Second Person of the Trinity made flesh was of course entirely orthodox. This doctrine had been proclaimed definitively at Chalcedon.

The article about Constance in the Catholic Encyclopedia offers a careful and detailed presentation of the circuмstances and pronouncements of this council, several aspects of which were pretty unappetizing.

Yeah but the condemned proposition is "Two natures, divinity and humanity, are one Christ.” not the rest of that. Could it possibly be erroneous to say the natures are Christ but proper to say the natures are aspects of Christ? I know we worship the divine essence but this is confusing.

A great many of the council's decrees were not approved. Gallicanism was rampant there, as it was a bit later at Basel. That is something you would have learned if you had read the article, as you were directed to. Stop wasting everyone else's time with childish questions you ought to be competent to investigate yourself.

It is true that not all the sessions were approved. But the condemnation of Hus' erroneous statements were indeed approved.

Pope Martin V, Council of Constance, Session 43, Inter Cunctas(Questions to be Proposed to the Wycliffites and Hussites): “Article 11. Likewise, let the especially learned person be asked, whether he believes that the decision of the sacred Council of Constance passed concerning the forty-five articles of John Wycliffe and the thirty of John Hus described above would be true and Catholic: namely, that the above mentioned forty-five articles of John Wycliffe and the thirty of John Hus are not Catholic, but some of them are notedly heretical, some erroneous, others audacious and seditious, others offensive to the ears of the pious.