The real question is whether 1 + 1 = 2 is true independent of us recognizing it. If the answer is no, then math really is just a system of ideas, and you’ve slipped into psychologism, where truth depends on minds.
But take one thing and then another: you have two things. That’s true whether or not anyone notices. Some mathematics is a human system of ideas, but some of it isn’t. Arithmetic reflects real patterns in the world. Logic, too, is not merely invention, it formalizes cause and effect. Numbers, in the Pythagorean sense, aren’t just marks on paper or symbols of order; they are the order inherent in reality, the ratios and structures through which the world exists at all.
At bottom, this debate is about the logos: what makes the universe intelligible at all, and why it isn’t simply chaos. When people say “math is real,” they mean it in the Platonic sense, not that numbers are rocks, but that they belong to the intelligible structure underlying reality.
God enters the picture not as a bolt-on explanation, but as the consequence of taking mathematical order seriously. If numbers and geometry are woven into reality itself, then the question isn’t whether math is real, it’s why the universe is structured so that it can be read mathematically at all. Call that intelligible ground the logos, or call it God; either way, it’s not an extra mystery but the recognition that reason and order are built into the world.
Calling math “just useful” misses the point. Why is the universe so cooperative with our inventions in the first place? The deeper issue is the logos: that the world is intelligible rather than chaos. That’s what people mean when they say math is real, not that numbers are physical things, but that the order they reveal is woven into reality itself.