Summary: The Ancient Greeks set out most of the questions that have been of interest to philosophers as well as many questions addressed by modern science.
The Pre-Socratic Greeks
The Ancient Greeks set out most of the questions that have been of interest to philosophers as well as many questions addressed by modern science. Philosophy and natural science were originally not regarded as separate areas of inquiry and early Greek philosophers focused on the question, now dealt with by modern physics, of what the universe is made of.
Thales (sixth century BC) believed everything was made from a single element, namely water. His student Anaximander concluded that there must be a single element that came before all other elements and which was infinite. He thought that this element was air. Anaximander was an early supporter of the idea of infinite regress which contrasts with the view that there must be a “first cause”.
Around the same time, Heraclitus thought fire was the source of all things but also that everything is in a state of flux. Different elements, sometimes contained within the same thing, come into conflict producing constant and ongoing change. This was an idea that seems to contain the seeds of the dialectical thought that would be subsequently adopted by Hegel and after him, Marx. Heraclitus also took an interest in human affairs. But like Plato who came after him, Heraclitus thought that most people were incapable of attaining wisdom.
Pythagoras (570 BC – c. 495 BC) was the first to argue that there was a structure to the natural world that could be expressed in mathematical formulas. This idea set the stage for modern physics. The connection Pythagoras made between mathematics and philosophy would also be of enduring influence.
Parmenides (515-450 BC) argued that change is an illusion and things continue to exist as they always have. He believed the universe had always existed and always would. It can never become “nothing”. Everything is one, unchanging and eternal. This view is known as ‘monism’ and the theory would subsequently be further developed by Spinoza. Parmenides was also the first to hold that four elements- earth, fire, water and air- in different proportions, make up all the substance of the universe, a view that formed the cornerstone of alchemy until the Renaissance.
Anaxagoras (500-428 BC) held that the universe began when everything was packed together in one mass. This view has an obvious similarity with modern scientific theory that the universe was contained in an infinitely dense singularity prior to the “big bang”.
Empedocles (490 – 430 BC) taught that living things started with body parts combining in different combinations, with only those surviving able to endure. Although his theory did not include successful adaptations to the environment his thinking obviously anticipates the development of Darwin’s theory of evolution.
Democritus (460-370BC) held that the universe is made up of atoms and empty space. Atoms are the tiny particles which make up everything and move around in empty space constantly changing in configuration. When a body decays its atoms are dispersed and reconstituted in another form. Democritus’s atom is an inert solid whereas modern science tells us that atoms interact via electric and magnetic force fields and are far from inert. Nevertheless Democritus, together with his teacher Leucippus, both appear to have correctly understood the basics of physics, even if their conclusions were reached through intuition, rather than experiment.
The Greek Philosophical Giants
The three giants of Greek philosophy are Socrates, Plato and Aristotle.
Socrates left no written work. He was a prominent critic of the Sophists, many of whom were professional advocates, and who held that there is no absolute truth and that all morality is relative.
“Sophistry” is now defined as the use of clever but false arguments, especially with the intention of deceiving. Socrates however believed the aim of enquiry should be to illicit truths. Nevertheless he adopted some of the methods of the Sophists through his constant interrogation of the assumptions underlying propositions. This approach still informs some methods of teaching and is similar to cross examination, the means used to try and elicit “truth” in the courtrooms today. 
Socrates was more interested in human concerns, or moral and political philosophy, than more abstract theories about knowledge. It took a long time, but this would also eventually come to be the tendency of modern Western philosophy.
Plato however concerned himself with theories of knowledge as well as moral and political philosophy. Indeed his political philosophy grows out of his theory of knowledge.
Plato’s theory of knowledge was based upon the notion of ideal forms. Thus there are horses of different types, colours, and sizes, but we have an idea of the form of the horse which applies to all horses. Plato sees this ideal form as constant, perfect and everlasting. It is separate from, and superior to, all the particular actual examples of the horse.
Plato believed that the ideal forms we can come to understand have an existence independent of the human body. He believed that all human beings have an immortal soul where ideas are located. This soul exists before we are born and lives on after death and the obtaining of knowledge is a process of remembering ideas that are already located in this soul. Plato said that the only way to acquire knowledge was through thinking or reasoning as opposed to experiencing things through the senses.
The highest of all the ideal forms is “the form of the good”. This is superior to all particular examples of good and all other ideal forms. The form of the good sits above all other forms of everything. It is, in a sense, like God.
Plato’s politics stemmed directly from his view that the ideal forms were only completely accessible to philosophers. In his allegory of the cave, Plato put forward his view that ordinary people were like prisoners trapped in the cave, only able to see shadows or images on the cave’s wall, rather than the light causing the shadows. If they ever left the cave the prisoners would be blinded by the light.
Plato concluded that common people have “no true knowledge of reality, and no clear standard of perfection in their mind to which they can turn”.He concluded that society should be organised around classes, with philosophers at the top and a virtuous and selfless military caste existing between the rulers and the common people.
Aristotle believed that knowledge was acquired by contemplation of experience derived through the senses. For example, rather than the notion of a horse being derived from a pre-existing ideal form, the notion is built up from examining actual horses and analysing their common characteristics. The same went for notions of justice or goodness.
Aristotle also proposed a system of logic whereby information in two statements constitutes premises that can be used to reach a conclusion.
Although he believed that knowledge was acquired through the senses and that the senses cease to function upon death, Aristotle maintained a belief that the soul is responsible for our thoughts, is immaterial and immortal.
Aristotle rejected crude materialism. A house, for example, is more than just matter. It has a plan and a builder. If somebody agreed to build you house and came and dumped all of the components of the house on your land, they would not have built you a house.
Aristotle identified four causes for how a thing comes about- these were a plan or blueprint (the formal cause), the material the thing is made from (the material cause), the maker (the efficient cause) and the broad purpose for which the thing is made or exists (the final cause).
In politics Aristotle identified three different forms of government and the ways in which each of these types of government could be perverted in the interests of a particular group.
In moral philosophy Aristotle is most famous for two ideas- the golden mean and virtue ethics.
The golden mean is best illustrated by example. For example, courage is a virtue. But too much courage is reckless and too little is cowardly. Thus Aristotle advocates something in the middle is best- this is the golden mean.
To understand virtue ethics one must first touch upon the two other main ethical systems known to philosophy- these are utilitarianism, sometimes called consequentialism, and deontology, sometimes called duty ethics.
Consequentialism determines right or wrong through consideration of the consequences of an action and how many people are affected either positively or negatively by it. Duty ethics judges right or wrong in terms of whether or not the person taking the action has intended to act in accordance with duties- which may be duties set down by God, or established, through reasoning processes which come to the conclusion that certain rules should apply universally.
Virtue ethics adopts a case by case approach with reference to what the action or decision says about the character of the decision maker. In many ways it seems a circular notion which does not really provide a reliable guide to action- an action is good if it contributes to personal virtue and a virtuous person will do good.
On the other hand, both duty ethics and consequentialsm also suffer their own problems and in some ways this may drive us back to case by case approaches.
Aristotle is also often regarded as the father of the theory of natural law. Natural law is the view that human laws might vary from place to place but that there also exists laws according to nature. Aristotle did not actually write much on the subject. But he did quote Sophocles and Empedocles suggesting that there were natural laws that were universal and which should bind every body, even in the absence of any specific agreement or contract.
The Greeks after Socrates, Plato and Aristotle
After Socrates, Plato and Aristotle Greek philosophy split into four main schools of thought- the Cynics, the Sceptics, the Epicureans and the Stoics.
The Cynics, typified by Diogenes, rejected conventional ideas of virtue and regarded wealth, power and honour as obstacles to virtue preferring a simple life free from material possessions. They were, so it seems, the original hippies.
The Sceptics, typified by Pyrrho, rejected the reliability of the senses in the same way as Plato. But they also rejected ideal forms as a basis for truth, asserting that every argument had an equally strong counter argument and that there was no philosophical certainty. But unlike the Sophists, many of whom were simply acting as advocates for clients, the Sceptics were regarded as having a genuine philosophical position; They never found themselves persuaded by any particular argument as to the true nature of things. The truth, if it existed at all, was elusive.
The Epicureans, who took their name from Epicurus, accepted the atomism of Democritus and rejected the idea of the soul, holding that physical death was the end of our individual existence.
Epicurus believed that we should focus on enjoying life rather than focussing on a non-existent afterlife and taught that “good and bad” should be judged by the pleasure or pain resulting from particular actions.
His emphasis on pleasure meant that Epicurus is forever remembered through the word “epicure’ the contemporary meaning of which is a person with cultivated taste, especially in relation to food and wine. But despite his promotion of pleasure, Epicurus was no glutton. He also promoted moderation and cultivation of friendship. His ideas are a precursor to modern secular humanism as well as the notion, subsequently developed by Bentham and Mill, that a good action should be judged on the basis of how many people derive pleasure or pain for it- utilitarianism.
The Stoics, associated with Zeno of Citium, taught that nature is the only reality and that we are part of it. The central idea is that we must learn to accept things over which we have no control and also control our destructive emotions. Virtue will foster the good life and lead to us not being affected by misfortune. Stoicism is regarded as having been the predominant popular philosophy or approach to life in the Roman Empire.
 ‘Philosophy in Minutes’, Marcus Weeks Quercus
 Philosophy in Minutes IBID, pg 58