It is common for people to scoff at tears as a behaviour and a subject of investigation. Tears are, they say, feminine, self-indulgent and melodramatic. It is not hard to notice, in those beliefs, the patriarchal assumptions about what should be valued and what should be mocked. Writing teachers will instruct students not to show their characters’ sadness through crying, calling it cheap. On the other hand, there are those who proclaim the necessity of “a good cry”, who indignantly defend weeping of all varieties and who see tearfulness almost as an identity. “I’m a crier,” they declare, praising its soul-cleansing effects. “Get over it,” their opponents instruct, demanding the shift toward progress and action that they believe crying prevents.

But rather than looking at tears with a predetermined belief in their value, or away from them in embarrassment or disgust, it can be clarifying to look through, into or around tears, to trace the small and large patterns that they create and reveal.

Not all tears are alike. The human body produces three kinds: basal, which form an oily layer over the eyeball to keep it from drying out; reflex, which appear when an eye is bothered by cutting onions or a speck of dust and needs to flush the irritant away; and psychogenic, which are shed for emotional reasons. Notably, emotional tears have a higher protein level than basal and reflex tears, which makes them thicker and causes them to fall more slowly.

This thickness intrigues me. The longer it takes for these tears to travel down a cheek, the greater the chance that they will be noticed by another person and their message perceived. Tears are a social signal.

Emotional tears fall more slowly, increasing the chance that they will be noticed. They are a social signal

Some people disagree, arguing that humans also cry alone. But even without a witness, tears streak outwards, seeking care. That message can be socially directed toward the self; sometimes a solitary crier will wrap their arms around themselves, creating their own soothing embrace. One might, in those moments, think of the poet Arthur Rimbaud’s declaration: “I is an other.” Sometimes, a person is the sender and the recipient of the crying signal.

What the social signal of tears makes happen varies from culture to culture and depends on the identities, access to power and beliefs of the crier and their witnesses. Think of the “school resource officer” who was called to the classroom of a crying seven-year-old African American boy and put the child in handcuffs. Think of the white police officer who cried in court when she spoke of killing an African American man in his home, and the hug she later received from the African American judge.

Tears often serve as a lubricant in the wheels of white supremacy. Many people (including Brittney Cooper and Ruby Hamad) have written about the harm of white women’s tears – how they have contributed to a long history of violence towards black people, indigenous people and people of colour.

Doctors have their own precise frames in which to interpret people’s tears. They can hang little paper tabs from a patient’s eyes to measure tear production, the slim rectangles slowly changing colour as the body does its work. When a psychiatrist is working to diagnose depression, she will ask a patient to describe his or her crying, offering a range of possibilities from: “I do not cry any more than I used to,” to: “I cry over every little thing,” before ending in numb dryness: “I feel like crying, but I can’t.” I am reminded of hypothermia, the growing, shivering pain that transforms just before death into a surprising warmth.

‘When my child was a toddler, she cried one day because the lemon she wanted to eat would not remain whole.’ Photograph: Jonathan Nourok/Getty Images

My depression has yet to reach that dry state. Instead, when an episode is at its worst, I can find myself shaking with cries for an hour after something as simple as dropping a knife to the floor. I am learning to say these things with what I hope is neither pride nor shame. But tears have a habit of magnifying and distorting. Their very nature – their emotional origins – makes it difficult to express these feelings plainly.

That is why I try, as much as possible, to say what tears do. Tears can form an intimate bond between people. They can also create a disgusted separation. Their effect depends largely on the degree to which people share common stories about who they are and how the world works.

I once read the claim that people sometimes cry from aesthetic experience, “such as the birth of a child or the unveiling of the latest Lamborghini”. Both examples bewilder me. I have gone through birth twice (once as child, once as mother) and I can’t figure out how it falls under the category of “aesthetic experience”. I should admit I have never seen a Lamborghini – newly unveiled or otherwise – but when I imagine one, I feel no inclination to cry. It is hard for me to imagine any possibility of connection with someone whose ideas of aesthetic tears differ so hugely from mine. Honestly, it is hard for me to imagine his tears at all. I have a feeling they are actually tiny Lamborghinis running down his face.

The tears that seem most full of potential are those that surprise by breaking out of expected and systemic patterns, revealing the small and strange undercurrents in which people daily resist larger tides. This kind of crying neither confirms what I already find emotionally compelling nor leaves me rolling my eyes. Instead, it points toward new possibilities for understanding, new combinations of ideas. When my child was a toddler, she cried one day because the lemon she wanted to eat would not remain whole. Why did this move me so? I think because, looking through the lens of her tears, the lemon became more real to me than it had been since my own toddlerhood. It was not a commodity, not a metaphor from which to extract a lesson about sweetness. It was utterly itself, brightly containing its wholeness and its destruction. An impossible lemon – of course she was crying.

Crying occurs when people have reached the limit of what can be said in words

Perhaps you have noticed that it is almost impossible to sing and cry at the same time. The throat muscles cannot simultaneously obey the command to shape notes and the command to hold themselves open to maximise oxygen intake (a command that crying provokes unconsciously). This leads me to believe that the opposite of crying is not laughter (those two, I would argue, are sisters), but song. As a poet and as a human living on a planet careering ever more deeply and unevenly into capitalism-induced horrors, I want to attend to both: the moments of singing; the moments when a voice breaks.

I have been thinking about breaking points a lot lately, in part because of a conversation with the Iranian-American poet Kaveh Akbar about the limits of the English language and all the violence that has occurred in its tongue. Recently, he sent me a lecture he had just given on this subject, delivered as the US again threatened Iran with war. He wrote that English is “a technology that has been used to promote and protect genocides, chattel slavery, ecological decimation, the building and deployment of nuclear weapons and more. That’s our paint.”

Crying occurs when people have reached the limit of what can be said in words and what they are capable of managing on their own. This does not mean that their words up to that moment are necessarily good or true or to be trusted, but it does signify that a breaking point has been reached. It means that it is time to pay attention to the systems the tears point towards.

The subject rewards that attention. Years into my research, I still found myself learning surprising new ways of understanding crying, physically and metaphorically. For instance, it turns out that the lump in your throat when tears are imminent is not a lump at all. Obeying the imperative to keep breathing through distress, the muscles of the throat work to stay open. When you try to swallow, the muscles resist, creating the sensation of an obstruction. Some people find relief in this fact – that their throat won’t close up, that their body is taking care of them and bringing them much-needed air. What if we could look at crying in the same way – not as a stopping point, but a passageway? What if we could look through crying to understand the abundance of patterns – of joy, oppression, grief, beauty, violence and transformative potential – that tears have the power to reveal?

The Crying Book by Heather Christle is published by Corsair. To order a copy for £10.91 (RRP £12.99), go to guardianbookshop.com or call 0330 333 6846. Free UK P&P over £15; online orders only. Phone orders min P&P of £1.99.