There are three areas where a seventeenth-century Spinoza would almost certainly have expanded his system had he known modern science.
The first is predictive processing. Spinoza says that inadequate ideas are confused ideas and adequate ideas grasp causes. Modern neuroscience tells us why this matters. The brain is not a passive observer but a prediction machine that continually generates hypotheses about the world and updates them through prediction error. Adequate ideas, translated into this framework, are not ideas that mirror reality perfectly but predictive models that are increasingly constrained by reality. That makes Proposition 18 much more biologically intelligible.
The second is entropy, and I actually this may be the deepest missing piece in Spinoza's philosophy. Spinoza speaks of conatus, the striving to persevere in existence, almost as though it were a metaphysical principle. Today we can place it within thermodynamics. Every organism is an island of low entropy that survives only by continuously importing energy and exporting entropy into the environment. Life is not merely "trying to exist." It is constantly fighting physical disintegration. Aging, disease, fatigue, and ultimately death are consequences of this battle. Will to life is therefore not simply a philosophical principle. It is the biological expression of thermodynamic necessity.
The third is what is zero-sum inverse theory, or more broadly, the recognition that life often unfolds under conditions of unavoidable trade-offs. Be a little more cautious with the terminology, because not all of biology is zero-sum. Cooperation, mutualism, and niche construction are also fundamental. Spinoza often writes as though an increase in one individual's power is simply an increase in perfection. Modern ecology shows that this increase is embedded in networks of finite energy, matter, and opportunity. One organism's success often changes the adaptive landscape for others. The world is full of trade-offs that are not moral failures but structural features of finite systems.
Spinoza's world
Conatus → Adequate understanding → Greater power → Greater joy.
A contemporary world
Entropy creates continual threats to order. Evolution builds predictive organisms to resist those threats. The nervous system continually updates models of reality to regulate the body. Better models often increase the organism's ability to survive and flourish, but they do so within ecosystems where resources are limited and other organisms are simultaneously pursuing their own conatus. Consequently, greater understanding may increase effectiveness without guaranteeing either happiness or universal benefit.
It is fascinating that, despite these corrections, Spinoza's central intuition survives. He sensed that understanding the causal structure of reality changes how we live. What he lacked were the mechanisms. Evolution explains why organisms strive. Thermodynamics explains why striving never ends. Predictive neuroscience explains how nervous systems generate experience and learn. Ecology explains why flourishing is always relational rather than isolated.
If we were to write a single sentence that updates Spinoza after three and a half centuries of science, it could be like this. Every living organism is a thermodynamically fragile, evolutionarily shaped prediction system that continuously models its environment in order to resist entropy. The more accurately those models track the causal structure of reality, the greater the organism's capacity to regulate its own existence. Yet because all organisms exist within finite ecological networks, one organism's increase in power may support, ignore, or diminish the power of others.
This preserves the spirit of Spinoza while incorporating Darwin, Schrödinger's insight that life feeds on "negative entropy," modern ecology, and predictive neuroscience. It also explains why reality can be both lawful and tragic at the same time.
