Knowledge can come only from four sources, which should be on your fingertips and recallable.
i) Observations
We observe reality through our five senses and collect raw data from our environment. Observation means directly receiving information about a phenomenon through our senses. We can observe a situation, an event, an object, another person's behaviour, or even another person's physical or emotional state without personally experiencing that situation ourselves.
For example, I can observe that someone is crying, observe that someone is injured, or observe that it is raining. These are observations because I am receiving information through my senses. I can observe another person's pain, but I cannot experience their pain merely by observing it.
Observation therefore provides us with raw data about reality, but what we observe is limited by the capacities of our senses and by the particular circumstances under which we make the observation.
ii) Experiences and Experiments
Experience is different from observation. You can observe another person's situation, state, behaviour, or experience without experiencing it yourself. Experience requires personal interaction with or participation in a situation.
If someone is injured, I can observe their injury, but I do not experience their pain. If I myself am injured, the situation becomes part of my experience. If I stand in the rain, I experience being in the rain; if I merely watch someone standing in the rain from a window, I observe their situation.
Experimentation is a deliberate form of interaction with a phenomenon. We manipulate or reproduce conditions to see whether the same results are produced. If I want to determine whether a particular material expands when heated, I can heat it under controlled conditions and measure the change. If I repeat the experiment under the same conditions and obtain the same result, I have accumulated experimental evidence concerning that phenomenon.
Experience and experimentation therefore allow us to interact with reality rather than merely observe it.
iii) Collective Accounts of Observations and Experiences
History, archives, scientific records, testimonies, documents, and other forms of collective accounts are essentially accumulated records of the observations and experiences of people belonging to particular times and spaces.
When you read a historical account of a war, for example, you are not directly observing or experiencing the war yourself. You are reading an account based upon the observations and experiences of people who lived through that particular historical context, along with the conclusions that historians have drawn from the available evidence.
Collective accounts therefore extend our knowledge beyond the limits of our own individual observations and experiences. We cannot personally experience everything that has happened in the past, nor can we personally observe everything happening around the world. We therefore depend upon the recorded observations and experiences of others.
However, a collective account is still an account of observations and experiences rather than direct access to the phenomenon itself. We therefore have to examine the reliability of the account, the evidence upon which it is based, and the inferences made from that evidence.
iv) Logical Inferences
Logical inferences can be of three types: induction, deduction, and abduction.
a) Induction
Induction occurs when we gather a sample, identify a pattern within that sample, and induce a conclusion from that pattern. In principle, the greater the sample, the stronger the conclusion, although induction can give us probabilities rather than certainty.
Suppose a researcher examines the water quality of twenty wells in a particular region and discovers that nineteen contain a particular contaminant. The researcher may induce that wells in that region are likely to contain the contaminant. If the researcher examines hundreds or thousands of wells and finds the same pattern, the inductive conclusion becomes stronger. Yet it remains probabilistic because the sample, regardless of its size, does not logically establish that every well must contain the contaminant.
Induction therefore moves from observed particulars towards a general conclusion, with the strength of that conclusion depending upon the quality, size, and representativeness of the evidence.
b) Deduction
Deduction occurs when an established principle is applied to a set of premises in order to derive a conclusion. In principle, if the premises are true and the logical structure of the argument is valid, then the conclusion must be true.
But there is an important distinction here between validity and truth.
A deduction can be logically valid while still producing an untrue conclusion if one or more of its premises are untrue.
For example:
All metals that are placed in water sink.
This object is made of a metal that is placed in water.
Therefore, this object sinks.
The conclusion follows logically from the premises, so the structure of the deduction is valid. But if the first premise is false, the conclusion is not thereby established as true.
This distinction is essential because people often assume that a logically structured argument must produce a true conclusion. Logic can establish that a conclusion follows from premises, but logic by itself cannot make false premises true.
Therefore, when evaluating a deductive argument, we have to examine two things separately: are the premises true, and does the conclusion logically follow from them?
A valid argument can therefore have an untrue conclusion when its premises are untrue. Conversely, an argument can sometimes arrive at a true conclusion through faulty reasoning, but the truth of the conclusion does not make the reasoning valid.
Deduction therefore requires both sound premises and valid inference if we want to establish truth.
c) Abduction
Abduction occurs when we use contextual clues to arrive at the most reasonable explanation for the evidence available to us. In principle, these are educated guesses.
Suppose you enter your office in the morning and find the floor wet, the window open, several papers scattered across the room, and water droplets on the desk directly beneath the window. You may conclude that rain entered through the open window during the night.
But that is not the only possible explanation. Someone could have spilled water, a pipe could have leaked, or someone could have deliberately poured water onto the floor. The explanation involving rain may simply be the most reasonable one given the available evidence.
This is the nature of abduction. We move from an observed result towards a possible explanation. The conclusion is therefore provisional and can be replaced when new evidence provides a better explanation.
Everything You Read Can Be Reduced to These Four Sources
Every book that you read is basically an account of observations and experiences of its author, and the author would induce, deduce, or abduct conclusions from these observations and experiences.
Likewise, a history book is basically a collective account of observations and experiences of particular people in a specific time and space, together with the historian's inductions, deductions, and abductions from the available evidence.
A scientific paper, a historical document, a philosophical argument, a newspaper article, a biography, or even an ordinary conversation can therefore be examined through these four sources.
Observation provides the raw data.
Experience and experimentation provide personal interaction with reality and the opportunity to reproduce or test phenomena.
Collective accounts preserve and transmit the observations and experiences of others.
Logical inference allows us to construct conclusions from what has been observed, experienced, and recorded.
Everything that you read can therefore be reduced to these four sources of knowledge.
Now, your task is to see if all that you know, believe, and hold as true or false stands up to these criteria. If it does, test it further through your own observations, experiences, experiments, and inferences.
Ask yourself where the belief came from.
Was it something you actually observed?
Was it something you personally experienced or experimentally verified?
Was it an account of someone else's observation or experience?
Or was it an inference drawn from available evidence?
And if it was an inference, was it an induction, a deduction, or an abduction?
You would discover that more than half of what you knew to be true was basically premised in imagination, fantasy, or sentiments. These can be beautiful features of art and literature, and they can have immense value when appreciated in their right place, but they cannot serve as sources of knowledge.
A beautiful idea is not necessarily a true idea.
A deeply felt sentiment is not necessarily evidence.
A powerful imagination is not necessarily an observation of reality.
If we want to distinguish what we know from what we imagine, feel, or believe, then we must return to these four sources and ask what exactly our knowledge is standing upon.