Adaptive vs fixed flashcard intervals names the gap between a study tool that adjusts its review dates from your personal performance and one that walks every card through the same published ladder of days. In a fixed-interval deck, every correct recall moves a card to the next bucket in a disclosed schedule — for example, after 1 day, then 2 days, then 4 days — and a wrong answer always drops it back to the bucket that is due tomorrow. An adaptive scheduler, by contrast, recomputes each card's next due date from your history, the difficulty of the card, and often a formula such as SM-2 that can push a single card weeks or months ahead. The transparent fixed model has a different appeal: the rules are auditable before you start, the next due date is predictable, and the deck's behaviour cannot drift because a hidden weight changed under you. Disclosure matters most for casual learners who want to know exactly why a card came back today and when it will next appear, rather than trusting a black-box curve. Vocabulary Flashcards (Spaced Repetition) sits squarely on the fixed side of that comparison, with every rule visible on the page and the underlying lexical data traceable to two named reference works.
What "Adaptive" and "Fixed" Intervals Actually Mean
A flashcard interval is simply the gap between two reviews of the same card. "Fixed" means that gap is a published constant that does not change from session to session or from learner to learner. "Adaptive" means the gap is recalculated for each card, usually from your history, the card's perceived difficulty, and often a formula such as SM-2 that compresses or stretches the next interval depending on how confidently you answered.
The two approaches differ on several practical axes that matter when you pick a tool:
| Aspect | Fixed schedule | Adaptive scheduler |
|---|---|---|
| Source of the next interval | A published constant, e.g. 1, 2, 4 days | A formula applied to your last grade and the card's history |
| Predicability per card | You can state today's next due date before grading | The next date only emerges after you grade |
| Behaviour under many cards | Same ladder repeated for every card | Easy cards drift toward long gaps, hard cards stay close |
| Auditability of rules | Rules are readable on the page | Internal weights and ease factors are usually hidden |
| Failure mode | Some over-reviews of cards you already know | Some cards can disappear for so long that you forget them |
Neither side is automatically better. Fixed intervals make the system honest and reproducible, which is useful when the goal is to learn exactly how a schedule behaves. Adaptive schedulers can be more efficient on large decks because they stop wasting time on cards you have clearly mastered, but their behaviour changes the moment the formula changes.
Inside the Three-Box Modified-Leitner Schedule
The Vocabulary Flashcards deck uses a fixed three-box schedule inspired by the Modified-Leitner system documented by MIT 6.031. New cards begin in box 1 and are due after 1 day. A correct recall moves the card to box 2, which is due after 2 days. Another correct recall moves it to box 3, which is due after 4 days. A wrong recall resets the card to box 1, where it is again due the next day. The deck calls its exact rules "Modified-Leitner" rather than claiming one universal interval table, which keeps the disclosure honest.
The intervals themselves follow a powers-of-two shape:
| Box after grading | Next due after | Effect of "Got it" | Effect of "Again" |
|---|---|---|---|
| Box 1 | 1 day | Promote to box 2 | Stay in box 1 |
| Box 2 | 2 days | Promote to box 3 | Return to box 1 |
| Box 3 | 4 days | Stay in box 3 (no further promotion) | Return to box 1 |
MIT 6.031 describes a Modified-Leitner model with numbered buckets and powers-of-two day intervals, and the University of York independently confirms the core direction: a correct recall promotes a card to a less frequent box, while an incorrect recall returns it to the first box for more frequent review. Both sources are cited inside the page, so the schedule can be checked against a real curriculum reference rather than against marketing copy.
How to Run One Fixed Cycle of the Eight-Card Deck
The deck contains exactly eight unique adjectives: lucid, prudent, resilient, concise, impartial, fragile, verbose, and biased. Their spellings and displayed ordinary senses come from Princeton WordNet 3.1 as the primary lexical source, and a dedicated Cambridge Dictionary entry independently cross-checks every card. Running one cycle of the deck takes only a few minutes once you know the rules.
- Open the deck and let the page identify today's due cards. The session captures one integer UTC day at startup so crossing a clock boundary during one card cannot produce two different schedules.
- Read the adjective on the front, say or think of its meaning out loud, and only then press Space or Enter (or tap Reveal) to show the back.
- Compare your spoken meaning with the source-grounded paraphrase printed on the back. The short meanings are product paraphrases of the overlapping senses rather than copied dictionary examples, and they are tested literally.
- Press G (or tap Got it) if you recalled the meaning cleanly. The card moves toward the 2-day box and then the 4-day box on future correct recalls.
- Press A (or tap Again) if the meaning slipped, the wrong sense came to mind, or you only got close. The card returns to box 1 and becomes due again the next day.
- Work through every currently due card. When the last due card is graded, a summary shows cards reviewed, Got it choices, Again choices, and a recreational point total where each Got it is worth 100 points.
- Return on a later day to handle the new set of due cards. Progress is saved under one versioned key in local browser storage when storage is available, so the same browser on the same device will remember where each card sits.
- Use Restart only when you want to replay the schedule from a known state. Restart intentionally resets all eight local cards to box 1 and discards the saved box numbers and next-due days.
A Worked Transition Through Three Boxes
Because the schedule is fixed, the transitions are predictable once you know the start day. Suppose a card is currently in box 1 and you grade it on day 10. The promotion rule is "min(box + 1, 2)" against a zero-indexed bucket counter, with the next due day computed as the current review day plus two to the power of the new box. Working the arithmetic by hand:
- Day 10, box 1: press Got it. In the page's zero-indexed counter, displayed box 1 is index 0, so the new index is min(0 + 1, 2) = 1, which is displayed as box 2. Next due day = 10 + 2^1 = 12. The card is now box 2, due on day 12.
- Day 12, box 2: press Got it again. New box is min(2 + 1, 2) = 2 in the page's zero-indexed scheme (which corresponds to the third, 4-day bucket). Next due day = 12 + 2^2 = 16. The card is now box 3, due on day 16.
- Day 16, box 3: press Again. The card returns to box 1, and the next due day becomes 16 + 2^0 = 17. The card is due again tomorrow.
That single worked example is exactly the path the page's literal day-transition fixture pins, and it illustrates a feature that purely adaptive schedulers often hide: the next date is computable before you press the button, which means you can plan tomorrow's session from today's screen.
When a Fixed Schedule Is the Fairer Choice
Adaptive schedulers shine on very large decks where some cards become obviously mastered and stop being worth daily attention. For a deck of eight adjectives, that efficiency gain barely exists, and the transparency cost becomes the dominant factor. A fixed schedule is the fairer choice when you want the following: a rule you can state out loud before you start; identical behaviour across browsers, devices, and future versions of the page; and a clear answer to "why is this card due today?" that does not require reading source code or trusting an algorithm. It is also the right choice when the words themselves are short, common, and worth repeated exposure rather than fine-grained difficulty tuning.
For readers who enjoy the comparison shape and want a parallel example from another category, Adaptive vs Fixed N-Back: Which Route Should You Play? walks through the same adaptive-versus-fixed decision for a working-memory game, using a similarly transparent fixed route as the comparison anchor.
What the Eight-Card Deck Does Not Measure
The schedule is fixed, but the score is recreational. Each Got it is worth 100 points and each Again contributes nothing, so the summary at the end of a session is just a count of correct recalls for the current tab. The page explicitly states that no proficiency level, vocabulary size, grade, CEFR band, percentile, or educational placement is inferred, and that a small fixed deck cannot evaluate school readiness, employment fitness, fluency, a learning condition, treatment progress, or support needs. The deck is best read as a private recall game with auditable words and scheduling rules, not as a diagnostic. For formal language guidance or accessibility support, an appropriate qualified educational service is the right place to go.
The storage model also keeps the deck honest about what it remembers. The stored payload contains only the eight card IDs, their current box numbers, and their next-due integer days. It contains no account, name, email, free-text answer, language profile, score history, or device identifier. If browser storage is denied by a privacy setting, policy, quota, or private mode, the page continues with an in-memory deck for the current tab and says so. Restart intentionally wipes the saved payload and replays the schedule from a known state, which is useful when you want to demonstrate the rules to someone else without their seeing your previous answers.