**Mirrored from http://matrixeditions.com/Thurstonforeword.html**. Emphasis in foreword below not mine.

**Excerpt from Foreword by William Thurston** to

*Teichmüller Theory and Applications to Geometry, Topology, and Dynamics*

*Volume I: Teichmüller Theory*

by John Hubbard

I have long held a great admiration and appreciation for John Hamal Hubbard and his passionate engagement with mathematics. Hubbard has inspired me and many others. Passionate engagement is contagious. It shows through in his writing. This book develops a rich and interesting, interconnected body of mathematics that is also connected to many outside subjects. I commend it to you.

That’s the short version. Here’s a longer version:

**Mathematics is a paradoxical**, elusive subject, with the habit of appearing clear and straightforward, then zooming away and leaving us stranded in a blank haze.

Why?

It is easy to forget that mathematics is primarily a tool for human thought. Mathematical thought is far better defined and far more logical than everyday thought, and people can be fooled into thinking of mathematics as logical, formal, symbolic reasoning. But this is far from reality. Logic, formalization, and symbols can be very powerful tools for humans to use, but we are actually very poor at purely formal reasoning; computers are far better at formal computation and formal reasoning, but humans are far better mathematicians.

**The most important thing about mathematics is how it resides in the human brain.** Mathematics is not something we sense directly: it lives in our imagination and we sense it only indirectly. The choices of how it flows in our brains are not standard and automatic, and can be very sensitive to cues and context. Our minds depend on many interconnected special-purpose but powerful modules. We allocate everyday tasks to these various modules instinctively and subconsciously.

The term ‘geometry’, for instance, refers to a pattern of processing within our brains related to our spatial and visual senses, more than it refers to a separate content area of mathematics. One illustration of this is the concept of correlation between two measurements on a set, which is formally nearly identical with the concept of cosine of the angle between two vectors. The content is almost the same (for correlation, you first project to a hyperplane before measuring the cosine of the angle), but the human psychology is very different. Each mode of thinking has its own power, and ideally, people harness both modes of thought to work together. However, in formalized expositions, this psychological > difference vanishes.

In the same way, any idea in mathematics can be thought about in many different ways, with competing advantages. When mathematics is explained, formalized and written down, there is a strong tendency to favor symbolic modes of thought at the expense of everything else, because symbols are easier to write and more standardized than other modes of reasoning. **But when mathematics loses its connection to our minds, it dissolves into a haze.**

I’ve loved to read all my life. I went to New College of Sarasota, Florida, a small college that was just starting up with a strong emphasis on independent study, so I ended up learning a good deal of mathematics by reading mathematics books. At that time, I prided myself in reading quickly. I was really amazed by my first encounters with serious mathematics textbooks. I was very interested and impressed by the quality of the reasoning, but it was quite hard to stay alert and focused. **After a few experiences of reading a few pages only to discover that I really had no idea what I’d just read, I learned** to drink lots of coffee, slow way down, and accept that I needed to read these books at 1/10th or 1/50th standard reading speed, pay attention to every single word and backtrack to look up all the obscure numbers of equations and theorems in order to follow the arguments. Even so, when something was “left to the reader”, I generally left it as well. At the time, I could appreciate that the mathematics was an impressive intellectual edifice, and I could follow the steps of proofs. I assumed that such an elaborate buildup must be leading to a fantastic denouement, which I eagerly awaited — and waited, and waited.

It was only much later, after much of the mathematics I had studied had come alive for me that I came to appreciate how ineffective and denatured the standard ((definition theorem proof)^n remark)^m style is for communicating mathematics. When I reread some of these early texts, **I was stunned by how well their formalism and indirection hid the motivation, the intuition and the multiple ways to think about their subjects:** they were unwelcoming to the full human mind.