Spaced repetition memory systems make memory a choice

Memory is normally something which happens by chance. Often, it feels a bit like the object of a helpless prayer: you might be reading a book, and think to yourself “oh boy, I’d better remember this.”

One fascinating consequence of using a Spaced repetition memory system is that they make memory a choice. Once you’ve adopted a memory practice, if you want to remember something, you can simply cause it to happen: just take a few moments to write a question about it. Over the next few weeks, you’ll encode it durably into long-term memory. Moreover, it’ll only take you a few minutes cumulatively: Spaced repetition memory systems are extremely efficient. So not only do these systems make memory a choice, but they make the choice very low-stakes: Deciding to remember something with a spaced repetition system is a lightweight gesture.

This radically changes one’s relationship with memory! Core practices in knowledge work are often ad-hoc, and “remembering details” is a good example of a typically ad-hoc practice. But spaced repetition memory systems are an authentic Executable strategy for remembering specific details.

I often visualize this property embodied in a magic wand. When you feel an impulse of interest arise within you, you just point the magic wand at the object, and you’ll remember it effortlessly. It’s a tool which serves your intellectual excitement.

They’re not as great a strategy for solving People seem to forget most of what they read, and they mostly don’t notice, since it’s quite effortful to choose the details to remember and to write effective questions for an entire text. This is where the Mnemonic medium aspires to help.


Nielsen, M. (2018). Augmenting Long-term Memory. Retrieved from

Matuschak, A., & Nielsen, M. (2019). How can we develop transformative tools for thought? Retrieved December 2, 2019, from

Spaced repetition memory system

A spaced-repetition memory system combines the Testing effect and the Spacing effect to enable efficient memorization of many thousands of facts (Spaced repetition memory systems are extremely efficient). Some people also use them for a broader set of tasks (see below). Spaced repetition memory systems make memory a choice, but they’re not just for rote facts: Spaced repetition memory systems can be used to develop conceptual understanding.

The first consumer system of this kind was Supermemo, created by Piotr Wozniak. It adopted and popularized the term “spaced repetition”; prior literature had used a variety of terms (often referring to more specific facets of the underlying phenomenon).


Branwen, G. (2009). Spaced Repetition for Efficient Learning. Retrieved December 16, 2019, from

Who invented the name: spaced repetition? -

* I’ll summarize just the second experiment, since it’s more relevant to the kind of Spaced repetition memory system design I’m doing. Students who practiced via short-answer enhanced their recall the most relative to a control condition and a condition in which students simply read the correct answers. Short-answer-practicing students performed better than those who practiced via multiple-choice on a multiple choice post-test (d=0.41) but not significantly better than MC-practicers on a short-answer post-test.

  • [[Karpicke, J. D., & Smith, M. A. (2012). Separate mnemonic effects of retrieval practice and elaborative encoding. Journal of Memory and Language, 67(1), 17–29.]]
* Is the Testing effect produced by Elaborative encoding? When you review prompts in a Spaced repetition memory system, you give yourself an opportunity to form new connections based on your current context and the different thoughts you have during the review session.]]
* This paper attempts to produce a better scheduler for a Spaced repetition memory system by combining a model-based (per-student, per-item) estimator of student memory state, with a more holistic planning model which attempts to take students’ time constraints and test date into account.