Nothing is finite. How do you even know that 1 + 1 = anything? How do you know that you know the stuff that you think you know? Because in reality, the only that that you know for certain is that you exist: "I think, therefore I am." Everything else, you can never know for certain. It could all be fake.
Now I ask you two questions. See if you can answer them.
1. What are numbers?
2. Why does math apply to the real world?
1. Numbers quantify objects, linearly.
1 + 1 = 2 because a single object is quantified as one, and if there is another, the next in progression is known as two. We could count in binary and it would mean the same thing. After all, Dec 25 == Oct 31
2. Because everything is made of a finite number of elements.
You are missing the point. How do you know these things? Math might not even exist.
The philosophy of mathematics is, at its core, the study of mathematics from a philosophical perspective rather than a strictly mathematical one. Often times philosophers of mathematics concern themselves with the foundations of mathematics - what mathematics is, what kind of objects, if any it refers to, how we come to have knowledge of these objects, and how we are to think of mathematical objects and theories. Because the philosophy of mathematics often deals in foundations, in some senses it is a deviating branch of metaphysics and epistemology. However philosophy of mathematics is not just foundations - it includes questions about the nature of mathematical explanation, computation, proof, set theory, infinity and more. For this reason we will treat the philosophy of mathematics as a separate subfield, within the larger category of the philosophy of sciences and mathematics.
In the midst of a rather interesting discussion of the notion of Aristotle’s Unmoved Mover, Leah Libresco went on a mild digression about the philosophy of mathematics that I couldn’t let go of, and feel compelled to respond to. She says:
"I take what is apparently a very Platonist position on math. I don’t treat it as the relationships that humans make between concepts we abstract from day to day life. I don’t think I get the concept of ‘two-ness’ from seeing two apples, and then two people, and then two houses and abstracting away from the objects to see what they have in common.
I think of mathematical truths existing prior to human cognition and abstraction. The relationship goes the other way. The apples and the people and the houses are all similar insofar as they share in the form of two-ness, which exists independently of material things to exist in pairs or human minds to think about them."
The notion that there’s something special about math – that it has some sort of metaphysical significance – only makes sense if you ignore the history of how we uncovered math to begin with. It was, despite Leah’s protestations, exactly just the abstraction of pairs and triplets and quartets, etc. The earliest known mathematics appear to be attempts to quantify time and make calendars, with other early efforts directed towards accounting, astronomy, and engineering.
Mathematics is nothing more and nothing less a tool that’s useful for humans in solving particular problems. Math can be used to describe reality or construct useful fictions. For example, we know now that the spacetime we live in is non-Euclidian. But that doesn’t make Euclidian geometry useless for everyday life. Quite the contrary – it’s used every day. You can use mathematics to build models of reality that may not actually have any bearing on what’s real. For example, the complicated math used to describe how the planets moved in the Ptolemaic model of the solar system – where everything orbited in circles around the Earth – actually produced very accurate predictions. But it was also wrong. There aren’t actually trillions of physical dollars circulating in the economy – there are just symbols for them floating around.
The bottom line is that human beings have brains capable of counting to high numbers and manipulating them, so we use mathematics as a useful tool to describe the world around us. But numbers and math themselves are no more real than the color blue – ‘blue’ is just what we tag a certain wavelength of light because of the way we perceive that wavelength. An alien intelligence that is blind has no use for the color blue. It might learn about light and the wavelengths of light and translate those concepts completely differently than we do.
In the same way, since the only truly good mathematicians among the animals are ourselves, we assume that if we encounter other systems of intelligence that they’ll have the same concepts of math was we do. But there’s no evidence to base that assumption on. For all we know, there are much easier ways to describe physics than through complicated systems of equations, but our minds may not be capable of symbolically interpreting the world in a way that allows us to use those tools, any more than we’re capable of a tool that requires the use of a prehensile tail.
Math is a useful descriptor of both real and fictional concepts. It’s very fun to play around with and its essential for understanding a lot of subjects. But it’s just a tool. Not a set of mystical entities.
Here are some good readings on the philosophy of math:
Introductory Readings
Books
Stewart Shapiro - Thinking About Mathematics. Shapiro's book is a masterpiece of introductory philosophy - it's easy to read and covers nearly all the ground you would hope, starting with a brief gloss of the history of philosophy of mathematics and moving forward into the major schools of foundations, with equal focus on both the historical views (e.g. Russell/Whitehead, Frege and Brouwer) and contemporary movements (e.g. Hale/Wright, Field, Shapiro).
Encyclopedia Articles
As always the SEP is of great help. In particular, the following articles are essential:
Philosophy of Mathematics
Frege's Logic, Theorem, and Foundations for Arithmetic
Platonism in the Philosophy of Mathematics
Intuitionism in the Philosophy of Mathematics
Formalism in the Philosophy of Mathematics
Fictionalism in the Philosophy of Mathematics
Kurt Gödel
Set Theory
Explanation in Mathematics
Constructive Mathematics
Further Readings
Anthologies
Philosophy of Mathematics: Selected Readings ed. Benacerraf and Putnam - this is the bible of philosophy of maths, containing almost two dozen of the most important papers ever written in the subject. It's a bit out of date at this point, but still a classic. Rather than listing all of the must-read papers in the philosophy of mathematics one should just read this book cover to cover.
The Oxford Handbook of Philosophy of Mathematics and Logic ed. Shapiro - This book has articles on every major movement in philosophy of maths and logic written in a fantastically accessible way. It is a massive resource to anyone with interest in the field.
Primary Texts (Books)
L.E.J. Brouwer - Cambridge Lectures on Intuitionism
Richard Dedekind - Essays on the Theory of Numbers
Gottlob Frege - Grundlagen der Arithmetik or The Foundations of Arithmetic
Gottlob Frege - Grundgesetze der Arithmetik or The Basic Laws of Arithmetic. OUP has the first full translation of the Grundgesetze forthcoming, translated by Ebert, Rossberg, Wright and Cook. Reading it alongside Richard Heck Jr.'s Reading Frege's Grundgesetze is highly recommended.
Hartry Field - Science Without Numbers: A Defense of Nominalism
Bob Hale and Crispin Wright - The Reason's Proper Study
Stewart Shapiro - Philosophy of Mathematics: Structure and Ontology
http://www.reddit.com/r/philosophy/wiki/readinglist