EFFECTIVE RATIONALITY
Contents:
This is strongly tied to Rationality in Practice from Epistemology from Philosophy.
All truth or potential truths have only three bases:
Without any one, a statement is but an arbitrary claim.
All knowledge begins with the evidence of the senses.
Why? Because a “sense” is a point of contact (i.e. a point of direct interaction) between consciousness and the rest of reality. Thus, sense-perception is the only kind of input to consciousness given directly by reality. Hence, sense-perception is the most basic material of consciousness, and thus, the basic building-block of any knowledge (which is a conscious grasp of reality).
Causality determines how something exists and/or acts in a context.
Causality is the principle that a thing exists and acts as a thing is, i.e. a thing exists and acts as per its nature. Now, interaction is fundamental to anything worth worrying about in reality; if something can interact with nothing else, then it has no effect on reality, and thus, it neither can nor ever needs to be discovered, i.e. it is good as nothing.
By causality, since a thing exists and acts as per its nature, it must also interact with other things as per its nature. Furthermore, its nature in a given context can only be expressed by how it interacts with other things in the given context, since if it interacts with nothing, it has no means of having any effect and thus any expression in reality. Moreover, knowledge is based on interaction.
Hence, we have that:
For example, the nature of fire and its causal relationships with oxygen and the material being ignited can inform us about what would make the fire grow (e.g. more wood, more wind, etc.) and what would help it slow down or stop (e.g. blocking air supply as much as possible, moving away flammable items, etc.).
NOTE: Since everything exists and acts in a context and can only be grasped as such, knowledge is always contextual. Hence, it is key to keep the context in mind when applying generalisations. For example, knowing the general nature of fire, we can understand the basic contributors to its growth and decline, but just from this, we cannot understand how a fire may behave in a given environment, e.g. how a fire would spread across a forest, or how a fire may cause other effects on other materials such as cracking of clay or melting of ice. The point is that causal relationships and knowledge more broadly do not exist in isolation.
Facts can never exist in contradiction.
In other words, if a statement is such that denying it would contradict known facts, then it must be true, even if its contents have not been verified by direct observation or validated by the grasp of causal relationships.
For example (taken from Euclid’s Propositions), consider a triangle ABC with two equal angles ∠ABC and ∠ACB. Now, assume that the sides opposite to these angles, i.e. BC and AB, are unequal. Now, draw a line from point A perpendicular to BC. Let D be the point where it meets BC; hence, this line would be AD. Now, note that the sine of ∠ABC is AD/BC, while the sine of ∠ACB is AD/AB. Since BC and AB are unequal, AD/BC and AD/AB are unequal, and thus, the sines of ∠ABC and ∠ACB are unequal. But ∠ABC and ∠ACB are equal; let us say both measure to k. Hence, we have that the sine of k is two unequal values, which is a contradiction, since logically, one angle has only one measurement of sine. Hence, since facts can never be contradicted, and since the contradiction was drawn from the assumption that the opposite sides of equal angles in a triangle can be unequal, as must declare the assumption to be false, and its logical opposite to be true, namely that the opposite sides of equal angles in a triangle must also be equal.
If something is not based on truth insofar as it can be grasped by the senses or by reason, it is arbitrary. It is as simple as that.
The complexity arises when applying observations and logic to areas of uncertainty, particularly with indirect evidence from word-of-mouth, articles, specialised research inaccessible to the broader public, etc. How to judge things we cannot directly observe but must still make decisions about, such as professional advice (which can be hard to validate for someone not in the field), the intentions of a person, the operations of a business supplying you food, etc.?
The answer seems deceptively straighforward: the principles of truth-seeking. Why must this be the answer? Because logically, any rational decision made on any area must be based on rational principles, i.e. the principles of truth-seeking. But how? A thorough exploration on the nature of knowledge, certainty and evidence is presented in Knowledge and Certainty from Epistemology from Philosophy, but given below is the gist of the answer.
Observe:
Observe what is being said or done, and see how it relates to your first-hand observations. For example, the advice on muscle training may relate to your observation that repeatedly doing a task makes your body adapt to it better. As another example, the assumption that a person means you no harm may relate to your knowledge of his habits.
Find causal relationships:
Can you see causal relationships or likely causal relationships between facts you know first-hand and things you do not know first-hand? For example, you may grasp the validity of the scientific method, and thereby have greater trust in the results of those who teach it, preach it and aim to practice it. As another example, you may grasp the incentives of a business, the variety of people involved in it with aligned motives (since trade cannot happen if motives do not align in some way), and the way these factors go against the act of trying to sell customers poison for food.
Logical necessity:
What things you do not know first-hand are in fact logical extensions, or at least likely logical extensions, of things you do know first-hand? For example, if you know someone has a very strong conscience and is tormented by guilt when he goes against it, then you could determine that he likely did not commit a theft he is accused of. As another example, if you know that an electric motor can produce maximum torque instantaneously, then you could determine that a key problem in designing an electric vehicle is not in acceleration but in controlling acceleration.