Penluma
Deep, worked-through writing on systems, AI, money, and thinking clearly.
Pen + lumen — the light of the pen. Each topic goes from plain-language intuition, to precise mechanics, to the failure modes that show up in the real world.
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View all 519 →Welcome to Penluma
Penluma comes from pen + lumen — the light of the pen. Writing is how unspoken thoughts come into view: vague intuitions become precise, and precise ideas…
The Real Challenge: Why AI Tutors Are Not Teachers Yet
If you have ever asked a modern AI chatbot to "explain how the heart pumps blood" or "quiz me on Spanish verbs," you already know something surprising: it can…
What Instructional Design Actually Means
Imagine you hire two people to help your nephew pass a math exam. The first person knows math perfectly.
How Humans Learn: A Plain Tour of Memory
Before we can build software that helps a person learn, we have to understand the machine we are trying to help: the human brain.
Cognitive Load Theory: Why Too Much at Once Fails
Have you ever sat through a lesson, nodded along the whole time, felt like you understood everything, and then realized an hour later that almost none of it…
Knowing vs Understanding vs Remembering a Month Later
Imagine two students. Both finish your AI tutor's full course on, say, fractions. Both clicked through every lesson, both passed every quiz at the end of each…
Retrieval Practice: Why Testing Beats Re-reading
Imagine two students preparing for the same exam. Anita reads the chapter four times, highlighter in hand, until every sentence feels familiar.
Spaced Repetition: Beating the Forgetting Curve
Here is an uncomfortable truth about being human: most of what you learn today will be gone within a day or two.
Interleaving, Dual Coding & Desirable Difficulties
Here is one of the strangest truths in all of learning science: the study methods that feel the best are usually the ones that work the worst, and the methods…
Bloom's Taxonomy: The Ladder of Understanding
Imagine two students who both "studied" the water cycle. Ask the first one a question and they can recite "evaporation, condensation, precipitation" perfectly.
Mastery Learning and the 2-Sigma Problem
Imagine two students sitting in the same classroom. The teacher explains long division, the class moves on to fractions the next week, and one student quietly…
Zone of Proximal Development, Scaffolding & Worked Examples
Imagine you are teaching a child to ride a bike. Some things are already easy for them: sitting on the seat, holding the handlebars.
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The Penluma story
Penluma is pen + lumen — the light of the pen. It started as a personal research habit: going deep on one hard topic at a time and writing until the fog cleared. These are the evergreen results, published so they can help others learning the same things. New topics get added all the time.