Adapted from my work-in-progress guide to brain and behaviour, Neurotypica
Rational thinking is something of a gold standard for many of us. A singular goal held-over from the Age of Reason. But there's something diseased about the way we conceptualise rational thought. I'll quote myself:
Historically, emotion has been viewed as the enemy of reason. Emotions make us act without thinking. Plato described emotion and reason as the horses that pull us in two directions. The biblical prophet Isaiah encouraged us to come together and reason, rather than act without thinking. A crime of passion was once a legitimate excuse for murder. ... Even modern approaches to therapy often position emotion as the enemy of rational wellbeing.
You see, there's something that really scares us about emotions. We have some idealised version of ourselves that lives emotion free---flesh made automata---that we're trying to achieve. We should really cut that shit out, because there's no such thing as action without emotion. It doesn't make any sense.
A quick neuroanatomy primer
We love the brain. The brain is the seat of rationality. If only we could get rid of all this other messy plumbing, leaving behind this paragon of evolutionary development, then maybe we wouldn't have to deal with emotions at all, right?
Obviously not, or I would be writing this acerbic intro. You see, the brain is merely an extension of the evolutionarily ancient nervous system. A nervous system helps coordinate perceptions and actions. The more complex the nervous system, the more perceptions and actions are possible.
Information comes in through our senses, it travels from nerves at those sites following pathways that journey through the spinal cord, the brain stem, and then often a structure roughly in the centre of your brain called the thalamus. From there, the brain is made available for this information to travel---the thalamus is often called the 'relay station' of the nervous system. From the brain, the information will be transformed from the perceptual information it came in as to the motor (movement) information it needs to go out as so we can deal with our environment. Along the way, it will grab things it needs from various regions and networks in the brain, like memories and relative value and whatnot.
That information will travel more or less of this journey, depending on the complexity of information. For example, some reflexes never need to go all the way to the brain. When the doctor taps your knee, your spinal cord has all the information it needs to send an impulse to kick back to your leg. Some information needs to spend quite some time in the brain, undergoing various transformations, to be useful.
We often distinguish between the central nervous system (CNS) and the peripheral nervous system (PNS). The spine and the brain form the CNS---the highway from the senses to the brain and back again. The peripheral nervous system feeds the central nervous system, acting as a bridge from your spinal cord to your senses. It feeds in information about the world and information about the body.
But the peripheral nervous system is much older than the central nervous system, and it can do plenty of processing all by itself. It was the brain before brains were a thing, and as such it rents out its own space in this much newer structure everyone makes such a fuss about---it gets 'grandfathered' in, so to speak.
There is nothing that the central nervous system does that isn't mediated by the peripheral nervous system. The PNS has first contact with the information, and the CNS and PNS are married to one another all the way along that information's journey to the brain and back.
To put it another way, many people will say that the central nervous system is about voluntary action and the peripheral nervous system is about involuntary action. But for our purposes, we must understand that there is no such thing as voluntary action without at least some influence of involuntary action, from the way our senses work, to the peripheral nervous system's intense concentration on homeostasis---keeping our body in balance---to the fact that vast majority of our behaviour is reflexive and automatic.
Emotions and actions are one
A primary role of the PNS is to inform the CNS about the state of the body. We could call this something like a 'perception' of the body, similar to a visual perception or an auditory one. Another kind of sense.
This particular sense helps us to understand what is worth paying attention to in the world. In very brief terms, what is good and what is bad. This is related primarily to homeostasis---keeping the body in balance. So at the same time as we see or hear or feel something, we also get a visceral sense of what that means for our body. Food is good when we're hungry, and otherwise uninteresting. Rotten food is bad all the time. You feel these kinds of things in your body. This particular sense is a precursor to emotion. In fact, the distinction is arbitrary. There's no reason not to call this an emotion at all.
This feeling is then sent to the CNS for additional processing. Here is where we get a more nuanced picture of things---it's not just bad, but scary, or it's not just good, it's sexy, and so on.
The important approximation here is that it is hard to imagine a time in which there is perception without some kind of emotion, if only that very preliminary, visceral sense that emanates from the body via the PNS.
The second is that there's no reason to do anything all unless there's an emotion surrounding it! Why pay attention to the world unless it has some meaning? And what would be the meaning, if it wasn't an emotional meaning?
This is particularly important when we start to talk about 'rationality' and other such concepts. If you suspect that the way you feel and are planning to act is not 'rational', but rather 'too emotional', you might decide to do something else. But that something else is still grounded in some kind of emotion---the idea that somehow it's more 'good' to do something else. This sense of 'goodness' comes from the same systems that generated your more impulsive pattern of thinking. All you've done is decided to make one kind of emotional decision over another! It just might be that you're taking into consideration some different input for that emotional decision. Perhaps thinking of some imaginary future which is more powerful or motivating than the events of the present.
So, a third important approximation is that there is probably no kind of action without emotion.
No perceptions, no actions, no decisions, come without emotional baggage.
And all of those things are related to how your body remembers the environment---how good and how bad have those perceptions been in the past. Or alternatively, how good and bad you might anticipate them being in the future. This, in fact, is the reason why humans can be so hard to predict.
Outro
The undertone of our fear of emotions is that some are more urgent, more passionate than others. These emotions can be wonderful---new love, the folds of flab on a baby's leg, puppies in a window---but they can also be scary---rage, fear, shame.
When we seek rational thought, we're actually speaking to those less immediate and more future-oriented emotions. These emotions are slower, and feel less binding.
But emotions are all, in the end, motivators of behaviour. And those motivations are borne of our history of being in the world, both in our own lives and in our evolutionary past. It's always worth asking yourself whether you're really that equipped to choose better. I'd suggest, in many cases, you are not.