Skepticism Regarding Our Reason

by David Hume

The Weakness of Our Mental Powers Creates Uncertainty in Our Understanding of Truths

In all demonstrative sciences, the rules are certain and infallible.

But when we apply them, our fallible faculties depart from them and make mistakes.

So we must:

• create a new judgment to check our initial belief, and
• enlarge our view to comprehend the history of all the instances when our understanding has deceived us.
• Our reason is a kind of cause.

The truth is its natural effect.

But the truth is frequently prevented by:

• the bursting in of other causes, and
• the inconstancy of our mental powers.

Through this, all knowledge degenerates into probability.

This probability depends on:

• our experience of our understanding, and
• the simplicity or intricacy of the question.

No mathematician will:

• place an entire confidence in any truth immediately on its discovery, or
• regard any truth as anything but a probability.

His confidence:

• increases each time his friends approve of his proofs, and
• increases to perfection by the universal assent of the learned world.

This gradual increase of assurance is: nothing but the addition of new probabilities, and derived from the constant union of causes and effects, according to past experience. Merchants seldom trust the infallible certainty of numbers in any important and long business computation.

To solve this, they use the the artificial structure of the accounting. Accounting creates a decent probability of the correct computation that is beyond the accountant’s skill and experience. The accounts, of itself, has some uncertain and variable probability which depends on: the accountant’s experience, and length of the account.

Our assurance in a long computation cannot be higher than the probability of getting the correct computation.

I affirm that we are more secure in shorter computations than long ones.

The simplest equation is the addition of two single numbers.

We can easily reduce the longest series of addition to this simple equation by gradually reducing the numbers.

Thus, it is impossible to:

• show the precise limits of knowledge and probability, or
• discover that specific number where knowledge ends and probability begins.

But the nature of knowledge and probability are so contrary and disagreeing.

They cannot run insensibly into each other.

They must be entirely present or entirely absent because they will not divide.

If any single addition were certain, every other addition would be certain.

Consequently, the total sum would be certain, unless the whole can be different from all its parts.

I previously said that addition could be made certain by reducing the numbers.

But I clarify that the addition must reduce itself, as well as every other reasoning.

It would then degenerate from knowledge into probability.

All knowledge:

• resolves itself into probability, and
• finally becomes of the same nature with that evidence we employ in common life.