Philosophy, as we see, necessarily co-evolved with religion and politics in society. To survive, early symbolic philosophers rapidly learned to focus on the dirty job of answering ``unanswerable questions'' that had fallen through the cracks of the prevailing religion and hence didn't provoke a short trip to a stake surrounded by highly flammable material (or to an altar to have your heart ripped out, or to a prison cell where you would die of disease and malnutrition forgotten by all other humans, or...). Philosophers learned that religions didn't usually care about geometry, for example, and that geometry was useful. It was also fun to work on (for those people with the right kind of brain) and got a lot of attention as a kind of ``truth'' that didn't seem to depend on any particular things observed in one's sensory stream while still seeming to describe many of them.
Occasionally a particularly brave or stupid philosopher would take a stab at something more metaphysical (such as trying to invent an explanation for what everything was made of) or humanistic (such as working out social ethics on a ``rational'' basis). History contains many examples of philosophers who discovered the hard way that this led to a choice between voluntarily drinking hemlock or being burned at the stake to protect common folk from your heretical views and as an example to anyone foolish enough to believe that anything but the currently accepted system of social ethics and religious memes was the right one beyond question2.1 2.2
That is, to make a living at being a philosopher (and not get killed), it was soon found to be necessary to invent new questions that could actually be answered and that looked ``interesting'' in some way. One had to do so while creating the illusion of answering, or at least working on, the really hard ones, the big questions, all without offending the local political power (usually a King) or provoking the prevailing religious hierarchy by directly contradicting scripture. Indeed, to be truly successful, it was often necessary to have the active support of either the church or the crown if not both, and there are numerous examples of philosophers who survived in just that way.
As noted in the last chapter, logic and argument and rhetoric in general doubtless coevolved with (spoken) language itself, but real human language is pretty ambiguous and imprecise and arguments in it tend to be sustained at the alehouse level. One of the greatest discoveries in the history of humankind was that of the ``magic'' of algebraic manipulation of symbols that permitted the abstraction of concepts and relationships observed in and relevant to the ``real world''. As key elements of this discovery, philosophers invented two very important tools: Formal Logic and its more precise and abstract cousin, Mathematics, along with written language.2.3
Mathematics and Logic were immediately useful, of course - bookkeeping, monetary economics, the successful waging of war, the arguments of law, the engineering demands of architecture and winning at a variety of games of chance all relied on understanding and being able to manipulate numbers and shapes and verbal arguments based on historical records to guide future behavior. Some of the very earliest examples of written language are basically bookkeeping records, and large armies (as opposed to ``hordes'') have always required quantitative logistical planning to transport and support in the field. Verbal argument was doubtless a major component of successful business relationships and conflict resolution, and required a way of determining valid sequences of conditionally true statements as the argument was advanced to be successful.
Thus it was that the card-carrying philosophers of antique and modern times2.4 2.5 2.6 2.7 2.8 2.9 developed formal logic as the basis of a reasoning process they could bring to bear on questions both deep and abstract and immediately practical. Being (after all) clever, they also invented schools where they could develop and pass on their own small changes in the prevailing memetic schema directly to selected young humans, bypassing a lot of potentially dangerous review by religion and king - or better still educating the future priests and kings themselves within their schools - and creating a long ``social lifetime'' for their ideas. In this way new memes they invented sometimes served as nucleation points that would grow and actually be adopted by entire societies.
Formal logic (as will be discussed later) became a widely accepted memetic schema for determining truth value or formulating powerful arguments. It ws very simple and intuitive, but proved very powerful as a basis for symbolic reasoning.
Much of the basis for formal logic can be found in the so-called Laws of Thought, which date back at least to the aforementioned Parmenides, although the ones that we will study below are in a form attributed to Aristotle, who wrote prolifically and whose writings (for a variety of reasons) did a better than average job of surviving to today.
Incidentally, Parmenides had some really good stuff in the few of his writings to survive that were left out of Aristotle's Laws of Thought, in particular a concept of the void not at all incompatible with Zen's Mu (discussed below). This served as a precursor to concepts (such as that of a vacuum) that eventually became Natural Philosophy (in particular, Physics).
However, the language and world view of both Parmenides and Aristotle were unsurprisingly hung up by the idea of time (a situation that persisted until the last hundred years or so). Lacking a proper understanding of space-time as a single geometry, verb tense worked its way into the Laws of Thought where one would expect them to be time-independent and sequence-independent. Even today, one of the hardest things for students of physics to conceptually grasp is that in a relativistic Universe, time ordering and sequence are not what their classically trained perceptions tell them they are.
In fact, they are essentially classical laws in other senses as well and are in many ways blind to the possibilities of non-classical theories. As we will see, our notions of existence, causality, temporal sequencing, inference and more rely on many axioms which are not objects about which one can reason using the laws of thought, and which are, in fact, far from being ``obvious'' or ``self-evident truth'' the way they were for Aristotle.
Before we move on and examine the Laws of Thought, set theory, and logic itself, it is worth noting that both India2.10 and China2.11 were writing down theories of knowledge and rules for inference that were roughly contemporary with those of the Greeks. In both cases the actual rules very likely existed as oral tradition long before they were written down. The Indian rules, in particular, formed the basis for what might be called ``Buddhist Logic'' which is quite different from Aristotle's formal analysis of syllogism. In particular it focuses less on ``proof'' and more on fallacies and on ways of grading hypotheses. Its purpose seems to be the practical one of using their ``logic'' (perhaps better called ``reason'') to teach, to bring to the auditor of an argument conceptual or causal understanding of the subject at hand2.12.