All thought is reaction. Ideas do not “pop into our head,” though it may feel like it. They arrive there in answer to a summons: What do I think about X?

This is true for all creatures with a thinking function. Only humans, it appears, keep thinking beyond our need to know.

Henry seems a smart dog; he notes patterns and anticipates behavior. His big brown eyes gleam and fluffy head cocks adorably when he’s puzzled. He becomes in those decoding moments the very image of a sage. But having answered his question, he stops thinking. He does not ponder, wonder, speculate, envision places and time periods other than the here and now he inhabits. He does not compare, so does not regret, resent, aspire. He remembers – no creature can think without remembering – but how much he remembers beyond what he needs to isn’t clear. He does not dwell in the past – or the future – or the never-never land of what-if. His perplexity does not persist beyond its provocation. He never writes.

How, when, and why human consciousness broke out of the enclosure of the immediate into the limitless realms of was, will be, and what-if we’ll never know. Language played a part – and curiosity. I imagine in our pre-literate past a hirsute tot asking Dad, “What happens when we die?” and Dad making something up not to disappoint Junior, then it’s off to the races with religion, science, writing, the whole nine yards. Thinking proliferates quandaries which proliferate more quandaries ad infinitum ad nostram miseriam. Curiosity killed contentment if not the cat.

Brains like bodies come in all shapes and strengths. My hunch is that the key to intelligence is not comprehension but curiosity. I am not that smart. In school others grasped concepts and memorized faster than I. But I am very curious. I can’t not wonder. One thought leads to the next, one word to the next, which leads to fresh insights, realizations, questions. Writing unspools my thoughts like a ball of yarn. “What do I think about X?” I ask, and away my brain scoots like Henry on a scent. It amazes me how much I’ve learned by thinking. My thinking, unlike Henry’s, is impractical, haphazard and sometimes hazardous, but I can’t help myself. Thinking is my avidity, necessity, sport. Every word I write is a thought.

Humans have accomplished marvels by thinking: all invention is the product of thought. We’ve also gotten ourselves into hot water and eventually, I expect, will destroy ourselves. War, greed, and revenge are also thoughts. Noxious gases, too-tall towers, and AI are works of genius. A vote is a thought. Votes brought us the Nameless One who might single-handedly wreck mankind.

Thought can depress, discourage, craze. “Human kind,” wrote T.S. Eliot, “cannot bear very much reality.” What he meant is we can’t bear thinking about it. Henry can bear as much reality as he encounters, no problem.

When I’m tired, I think I’ve reached the end of thinking. The contents of my brain feel stale and unpalatable. One day my brain will stop thinking. I hope it goes out like a light and doesn’t slip-slide into disgusting dementia, but that’s not my call.

Then I sleep – and what do you know, my mind is brimming again, eager to browse and chew. Just now, awake from a deep nap (to a Bach toccata), I asked myself, “What do I think about thinking?” and here is the result. All these ideas have been thought before – “There is nothing new under the sun,” groused grumpy Ecclesiastes – but they’re new and tasty to me.