Here is the sentence in English:
And here it is in Latin:

Subjunctive and indicative are moods, not tenses, and it is relevant because it shows whether St. Thomas is saying something that he himself believes.

In English, when I say "I am a Catholic" I am stating a fact and using "am" which is indicative mood.  When someone says "were I a Catholic" he is referring something contrary to fact (he is not a Catholic) and using "were" which is subjunctive mood.  Latin uses the subjunctive much more than English and in many more grammatical constructions.

The phrase "quod terram esse rotundam per aliud medium demonstrat" has its verb "demonstrat" in the indicative which means the author believes it is a fact.  If he were alluding to something that he himself did not believe it would be in the subjunctive.  There is no ambiguity about this in the original Latin.

I accept these distinctions you are making. I too can understand grammar.

It doesn't necessarily indicate that St. Thomas believes it. Because it is part of the wider paragraph in which he is making a point about scientific proofs. While Latin does provide more precision in certain ways, it does not necessarily follow that St. Thomas was therefore making this his opinion. You are reading too much into it.

And thus being dishonest.

You said: "He would probably, however, no longer allow me to read trad forums.  Much more importantly, he would lose all respect for trads and our views on anything and probably stop attending the TLM with me."
So we have the smoking gun.  The reason you cannot be reasonable about flat earth.  Fear.  Fear of reprisal, fear of alienation, fear of people's opinions (beyond your husband's).  The fact is, you are afraid of being called stupid.  Yet that is exactly what you did to us in the beginning of this thread.  Yep, its all there in black and white.  Hopefully, there will be two lessons learned, fear not, cast not stones.  Oh, yea and a third one: earth is not a globe.    

Of course I fear failing in my duty to help my husband find salvation.  What a monster I would be if I did not.
But I don't know where you are getting these ideas about me fearing other things.

In the meantime, anything held by the entire Church for a 1000 years or more, is fixed truth, doctrine, and unchangeable.

Can you support this from an authoritative source?

One of the encyclicals teaching us how to understand Scripture and the Fathers was written by Pope Leo XIII.  If we were to reject his teaching, why would we even be trads?  For many (most?) of us, his condemnations of modernism are a key factor in recognizing the crisis in the Church.  I can't imagine that anyone, sede or otherwise, would accept his teaching on modernism while rejecting his teaching on Scripture.

But there would be a disturbing lack of docility in a Catholic who would reject an encyclical because it does not allow him to interpret Scripture as he wishes.  This is the attitude that led to the rise of Protestantism.

You have completely missed the point here. Either you are really clever or really stupid.

I was not suggesting that St. Augustine believed the earth is a ball.  It seems to me that the quote is saying that questions about the shape and form of physical objects are not a matter of faith and that it can even be harmful to the faith to talk about it too much.

It SEEMS that way because you have been too lazy to do real research into the flat earth. For those who understand the flat earth, they can clearly see he is talking about different models of the flat earth.

The Church rejected the pythagorean doctrine of the round earth, because it was long known to be an error. Go back to the quotes I gave.

We should care about the truth above all things. Which is why you are totally inconsistent, in defending corporal punishment and yet refusing to even look into the scientific proofs of the flat earth, and pertinaciously clinging to your BELIEF in the round earth against all the evidence.

I am not looking at science about flat earth because I do not expect to understand it.  I might be able to figure it out if I studied enough, but I do not care about it enough to make the effort.  It has no bearing on my salvation.

I am not looking at science about flat earth because I do not expect to understand it.  I might be able to figure it out if I studied enough, but I do not care about it enough to make the effort.  It has no bearing on my salvation.

Think for one moment about the absurdity of what you are saying.

You see the sky everyday, the earth everyday.

Some comes to you and says it is spinning at 1000 miles per hour, while going 65000 miles per hour (around the sun). That it is in the shape of a ball. That God is not above the sky, but at the edge of the universe which is billions of light years away.

Yet you can feel or see none of this. Your senses tell you the COMPLETE opposite. It is one of the most groundbreaking claims anyone can make to you in your whole life. Like telling you that your parents are not your real parents or that your country is not the country you thought it was.

But you remain indifferent.

That is called perversion. Which is contrary to nature. And is indeed a sin.

I accept these distinctions you are making. I too can understand grammar.

It doesn't necessarily indicate that St. Thomas believes it. Because it is part of the wider paragraph in which he is making a point about scientific proofs. While Latin does provide more precision in certain ways, it does not necessarily follow that St. Thomas was therefore making this his opinion. You are reading too much into it.

And thus being dishonest.

Honestly, you're all wasting too much time on what St. Thomas believed on this matter.  Whether he believed round or flat makes little difference.  What's at issue is whether the Church has pronounced on this subject.  In point of fact, the Magisterium has never even opined in favor of Flat Earth or Spherical Earth.  Indeed, there were some early Church Fathers who believed this, but the Providentissmus Deus quote amply demonstrates that a consensus on a scientific matter by the Fathers does not constitute the dogmatic consensus that's typically the hallmark of something being part of the Deposit.  It's quite possible, as Pope Leo teaches, that it was simply a function of the state of science at the time ... and not something revealed by Our Lord to the Apostles.  So this argument that it's Church teaching I find utterly unconvincing ... and much less that it's "heresy" to believe in a Spherical Earth.

I am willing to discuss this on its scientific merits but this idea that it's part of the Church's Magisterium I find to be preposterous.