Human thought is an amazing thing. It has given us not only science, literature, and morality, but also superstition, slavery, and war.
Your mental life involves a lot of different kinds of thoughts. You can make decisions about what to do, or figure out some truths about the world, or just daydream in a vivid series of images. There’s great diversity to the types of thoughts you can think.
Even so, we tend to think that you can only have one thought at a time. You can switch between different kinds of thoughts quite quickly, or you can think many thoughts one after the other, but you can’t think more than one thought at the same time.
That’s a mistake. There’s a way to think two thoughts at once. This isn’t something that a specialized, focused expert thinker does; we all do this often. I’ll explain how.
First, we must distinguish between mental actions and passive thoughts.
Sometimes you don’t direct your thought at all; your thoughts are just led, outside your control. This happens in mind-wandering, or when something you forgot suddenly comes to mind, or when you’re haunted by images that won’t go away.
(For more on mind-wandering, check out Zach Irving’s work, like this paper. For a careful discussion of the difference between mind-wandering and active daydreaming, check out this paper by Fabian Dorsch.)
But sometimes you do direct your mind; you can do things in thought. Things you do in thought are mental actions. You can remember your tenth birthday, or add 57 and 18, or imagine a blue horse in mental action.
Thinking two thoughts at once is possible when you engage in mental action that is intentional.
It’s a difficult philosophical question exactly how to define intentional action, but the concept of intentional action is not a technical term. We talk about intentional action all the time. Whether something is done intentionally matters to how we attribute actions to people, and to whether we praise or blame them for doing what they did.
Fortunately, we don’t have to worry about defining intentional action here. We can just rely on a couple of important facts about intentional action.
First: when you do something intentionally, you have in mind an idea of the thing you’re trying to do. For example, when you intentionally kick a ball to a friend, you think of kicking the ball to a friend. That’s your intention. The same point applies in mental action: when you intentionally recall your tenth birthday, you have in mind that you’re recalling your tenth birthday.
Second: when you do something in order to do something else, you can do several things all at once. Here’s an example from the influential late philosopher Donald Davidson. If you flip the light switch in order to turn on the lights—and the switch works, so that’s all you have to do to turn on the lights—then you have both (1) flipped the switch and (2) turned on the lights, and you’ve done both intentionally.
If we combine these two observations about intentional action, and apply them to mental action, we’ll see how you can think two thoughts at once in mental action.
When you intentionally do something in order to do something else as well, you still have in mind an idea of what you’re doing. Now it’s just a more complicated idea. In the Davidson example from above, if you intentionally flip the switch in order to turn on the lights, you have in mind flipping the switch, and you have in mind turning on the lights, and you have in mind the connection between the two: you think of doing the first thing as a way of doing the second thing.
Consider the same kind of case in mental action. If you’re J.K. Rowling writing the Harry Potter books, you can intentionally think of an insult in order to think of something Malfoy could say to Harry. If you carry out that (simple enough) task successfully, you can perform two mental actions at once: you (1) think of an insult and (2) think of something Malfoy could say to Harry. You can do them both at the same time because you are already thinking of whatever insult you’ll bring to mind as something that Malfoy could say to Harry. There’s nothing left over to do when you think of the insult in this context in order to think “that’s something Malfoy could say to Harry!”
Here’s a more mundane example. At a store, you could intentionally figure out which of two soap brands is cheaper in order to decide which soap to buy. In performing this mental task successfully, you can think “Soap A is cheaper” at the same time that you decide “I’ll buy Soap A.” You can do both at once since you already committed, at the outset, to buying the cheaper soap.
These complex intentional mental actions are ubiquitous. We perform them whenever we intentionally perform a mental action of one kind in order to perform a mental action of another kind as well. It doesn’t take extra effort, necessarily, and it doesn’t involve any fancy mental acrobatics that are only available to expert thinkers.
We should give up the misconception that all our thought is serial. You can think two thoughts at once. You already know how to do it, and you do it all the time.