Meaning Lives in the Reading Agreement
The last lesson left a question burning: cell 2 holds 65, and the cell offers no commentary — so what makes 65 a letter, a brightness, or an age? This lesson answers it, and the answer is arguably the single most important idea in the whole course. Once you own it, half of computing's "mysteries" — from garbled text to file formats to entire classes of attacks — become one idea wearing different coats.
The answer, stated plainly
Look for meaning inside the machine and you will not find it. The cell holds 65 — one number, no annotation (a cell holds one number and nothing else; there is no second compartment for "what kind"). The processor reads 65, moves 65, adds 65 — with no opinion (its action set contains no "understand").
Meaning lives in the agreement about how to read. "65 is the letter A" is true only under the text-reading agreement, where a table pairs numbers with characters. "65 is a brightness" is true under the image-reading agreement. "65 is grandfather's age" — under yours. The number is in the cell; the meaning is in the reader's contract with that number. Change the contract and the same cell, untouched, means something else entirely.