The Tetrahook System

Remembering precise historical dates is notoriously difficult. The brain is poorly equipped to store such information, especially when it lacks personal relevance. Even if we remember the details of an event, we often forget *when* it happened.

The Tetrahook System is a mnemonic technique designed to solve this problem. It works by encoding abstract date information as vivid, bizarre, and memorable mental scenes. By converting numerical data into symbolic images, and weaving those images into surreal visual stories, we bypass the brain’s weaknesses and instead utilise its strength in visual and spatial memory.

In this guide I shall present my system for transforming dates into memorable mental images. It’s based on combining pre-learned symbolic images (hooks) into rich, surreal scenes. Once a scene is fixed in your imagination, the date it encodes becomes almost impossible to forget!

The system is most likely to appeal to memory enthusiasts, but can be learned by anyone. It requires a little setup and practice at the outset, but the payoff is an unrivalled longterm precision in chronomnemonic recall.

Core Principle

The technique is built around the self-evident fact that the human mind remembers images more easily than it does numbers. By converting numbers and months into concrete visual hooks and combining those into unusual or emotionally-charged scenes, we leverage the brain’s natural strength in visual-spatial memory.

To achieve this, each date is split into two parts:

  1. Day and Month
  2. Century and Year

Both are visualised as pairs of interacting images and are then woven together into a single mental scene. The strangeness and specificity of the scene makes the original date easy to store in its encoded form, and – with a little practice – just as easy to decode back to the original date when required.,

The Three Hook Sets

To use the system, you must first memorise three sets of hooks (visual mappings of numbers, months, and centuries, to concrete visual images). This is where the initial effort must be made, but it is essential. These form the foundation of every encoded date.

The Standard Set

This set covers every number from 00 to 99. It is used for:

  • Days of the month (01–31)
  • The Year within a century (00–99)

Each number is assigned a specific object. For example:

  • 00 = boot
  • 01 = giraffe
  • 02 = swan

Producing your own set of hooks (as opposed to copying someone else’s) will make memorisation significantly easier, so I’ll leave that up to you. It doesn’t matter what the images are; the important thing is consistency and familiarity. Once learned, these 100 images become a powerful toolkit for encoding countless details, both within the Tetrahook System and within other mnemonic systems too.

The Month Set

This set includes 12 symbols, one for each month of the year. These should be as distinctive and evocative as possible. For example:

  • January = bells
  • February = chocolates
  • March = clovers

Try to select images that are already mentally associated with the month in some way – it will be much easier to memorise.

The Century Set

This set maps centuries (e.g. 1700s, 1800s, 1900s) to visual symbols. For example:

  • 1700s = steam train
  • 1800s = sewing machine
  • 1900s = cassette tape

This allows any year between 1000 and 1999 to be encoded as a combination of a Century image and a Year image (from the Standard Set).

Encoding a Date

Here’s the process in practice, using the eruption of Mount St Helens (18 May 1980) as the example event:

Step 1: Break the date into its constituent parts

Example: 18 May 1980

  • Day = 18
  • Month = May
  • Year (1980) → Century = 1900s, Year = 80

Step 2: Convert each part to images using the hook sets

  • 18 = leech (Standard Set)
  • May = bells (Month Set)
  • 1900s = cassette tape (Century Set)
  • 80 = cheese (Standard Set)

Step 3: Create visual pairs

  • 18 May = Leech + Bells = giant leeches attached to a large bell, ringing violently
  • 1980 = Cassette Tape + Cheese = tangled cassette tapes and molten cheese spewing from the volcano

Step 4: Compose a mental scene

Mount St Helens is erupting. A huge iron bell, infested with monstrous, writhing leeches, swings wildly as it tolls an alarm over the chaos. Molten cheese and tangled cassette tapes spew from the volcano, smothering the landscape in a tangled molten goo of melted cheddar and magnetic tape.