instrument · chapter II
The rules run out.
Explicit instructions achieve impressive results and stay brittle. Here is the whole problem in six rules.
Try the rules
6 rules · 7 junctions
- If it has a hole, it is a ring.
- If it has no straight sides and looks the same turned around, it is a circle.
- If it has three straight sides, it is a triangle.
- If it has four straight sides and sharp corners, it is a square.
- If it has more than four straight sides, it is a star.
- If it has no straight sides and sharp points, it is a crescent.
Pick a specimen to run it through the rules.
An educational illustration: a small rule system written for this exhibition, not a reconstruction of any historical program.
What you are seeing
The rules are a decision list: each one is tried in order, and the first that fits decides. That is how a great deal of early machine reasoning was written, as conditions and actions, and it works exactly as far as its author's imagination reached. The rounded square and the blob are not tricks; they are ordinary shapes the six rules never mention.
Adding a rule fixes the case in front of you and adds a junction to the chain. Every real system of this kind grew the same way, one exception at a time, until the list was longer than anyone could hold in their head. The rules here were written for this exhibition; they reconstruct no historical program, and the features (sides, corners, a hole, symmetry) were chosen to be readable, not complete.
The same system, still
Sources for the chapter
The history this illustrates is in the archive: Logic Theorist (1956), ELIZA (1966), the perceptron (1958) and Perceptrons (1969), each with primary sources on its own page.