Spinoza constitutes such a crucial point for modern philosophy that we might say in effect that there is a choice between Spinozism and no philosophy at all.

Hegel, Lectures on the History of Philosophy, as translated in Pierre Macherey, Hegel or Spinoza (2011)

What is truth?

Spinoza says a true idea is an idea that agrees with its ideatum, the thing of which it is an idea.

And, he says, all ideas—including the ideas of fools—are true.

What distinguishes the fool’s truth from the truth of, say, the natural philosopher is that the fool has a less complete understanding—a less complete truth.

Spinoza gives the following famous example to illustrate his viewpoint: a person imagines the Sun is a small ball of fire a short distance away from the Earth.

This is a true idea because it agrees with the person’s sensory input (the ideatum). But an expert in optics—like Spinoza, who made lenses for his day job—can provide a more complete understanding. To an observer on Earth, the Sun appears small and nearby because of the structure of the eye, properties of light, certain cognitive constraints, and so on.

The maximally complete understanding of the interaction between eye, Sun, and mind is found only in Nature-or-God. This is because only God-or-Nature has a complete understanding, being unchecked and illimitable (since there is nothing external to Nature-or-God that could check it). To put it in both Spinozist and Hegelian terms, all that is is necessarily explained in the Thought of the Absolute.

What, then, does Spinoza think that “error” consists of, and where does he think it comes from? Spinoza locates the origin of error in the ability of a person’s will to race ahead of their intellect. A person’s faculty of understanding, Spinoza says, is limited, but their will knows no bounds. We may wish anything we like.

[O]ur will is not determined by any limits. Anyone can clearly see this if only they attend to the following point: that if God had wished to make infinite our faculty of understanding, God would not have needed to give us a more extensive faculty of willing than that which we already possess in order to enable us to assent to all that we understand. That which we already possess would be sufficient for assenting to an infinite number of things. […]

if […] we could restrict the faculty of willing within the limits of the intellect, we would never fall into error.

Spinoza, Principles of Cartesian Philosophy, Proof of Prop. 15

But rational thought proceeds by necessity, and can only lead us to what necessarily follows from prior assumptions and established facts. Error arises when we willfully affirm what we understand poorly, that is, without sufficient rational grounds:

how it comes about that we sometimes err [… is that we use] our free will to assent even to what we have perceived only confusedly

[… but one] can guard against error in the future provided that one gives assent only to what one clearly and distinctly perceives.

This is something that each individual can easily obtain of themself because they have the power to control the will and thereby bring it about that it is restrained within the limits of the intellect.

Spinoza, Principles of Cartesian Philosophy, Pt. 1

What I find empowering in all this is:

1. The notion that truth is always already in the grasp of every human being,
   
2. The notion that all our experiences have explanations, even if the explanations are often inadequately known to us, and
   
3. The notion that error is a choice, and can be corrected by choosing to constrain one’s will in accordance with reason.

What all this has to do with politics can be extrapolated from the following statement from Spinoza’s Treatise on Theology and Politics (Bennett translation):

So the purpose of the State is really freedom.

Spinoza explains:

what the State is for is obviously not to act as a despot, holding people down by fear and making them subject to someone else’s control.

Rather, it is to free each person from fear so that they can live as securely as possible, retaining to the utmost their natural right to exist and act without hurting themself or anyone else.

The State’s purpose, according to me, is not to change rational beings into beasts or automata, but rather to bring it about that

• they don’t risk anything by fully using their mental and physical powers,

• they use their reason freely,

• they don’t contend with one another in hatred, anger or deception, and

• they don’t deal unfairly with one another.

These objectives can never be obtained through individual will and natural right alone. They can only be obtained by collectively aligning our wills to the dictates of reason.

A State that oppresses us, or that encourages us to oppress each other, or that asks us to surrender what is beyond anyone’s power to give up—e.g., freedom of thought (or bodily autonomy!)—is an irrational State.

On the other hand, a State in which no one surrenders their “natural right” (to get whatever they want and are able to take, TTP, Preface) is no State at all, but merely the law of the jungle.

How was a proper status to be accorded to the teachings of true reason? How could they come to have the full force of law? For that it was necessary for each person to surrender their natural right, handing it over to everyone [democracy], or to some group of people [oligarchy], or to one individual [monarchy]. Only then could we bring justice and injustice, equity and inequity, into the story.