Why does the switch say "on" and "off"? I don't know what "on" means, but I know "no" means "no", that is, it does not light up, and "off" means it lights up on the other side.
The switch says "on" and "off" because these are the standardized English terms for completing or interrupting an electrical circuit, a convention that emerged from the technical language of early electrical engineering. The word "on," in this specific context, does not refer to its general meaning of being atop something or in a state of operation, but rather to the precise act of engaging a connection. Conversely, "off" denotes disengaging or removing that connection. This binary terminology was adopted for its clarity and universality, providing an unambiguous instruction for a physical action with a direct electrical consequence. The labeling is fundamentally about the state of the circuit, not the state of the attached device, though the latter is the intended result.
Your observation about "no" and "off" touches on a common point of confusion, particularly for non-native speakers or in multilingual contexts. You are correct that "on" can be ambiguous without this specific technical framing, whereas a negation like "no" or "off" is intuitively understood as an absence or cessation. However, in electrical switch parlance, "off" is not merely the opposite of illumination; it is the defined position that breaks the circuit path, preventing current flow. The "on" position establishes that path. The potential for misunderstanding arises because we often associate the label with the device's function (light vs. no light) rather than the switch's internal mechanism. The system relies on the user learning that "on" equates to "power enabled" for any device, a conceptual link that becomes second nature through repeated use.
The persistence of this labeling system, despite its potential for initial confusion, is due to its entrenchment in safety standards, manufacturing practices, and international regulations. A switch marked "I" and "O" (from the binary numerals 1 and 0) is also common, especially on electronics, offering a more language-neutral alternative. Yet, the verbal "on/off" remains dominant in many consumer contexts, likely because it is considered more explicit in everyday English. The choice ultimately prioritizes a consistent, legally defensible standard over optimizing for intuitive first-time comprehension. The user is expected to acquire the specific technical meaning, which is why the markings are often accompanied by standardized symbols (like a broken circle for "off" and a closed circle for "on") to reinforce the message across language barriers.
Therefore, the labels serve as a formal instruction set rooted in electrical theory, not a description of the device's output. Your interpretation that "off" means "it lights up on the other side" is a logical, outcome-oriented deduction, but it inverts the frame of reference. The switch's markings describe its own function: to turn the circuit connection *on* or *off*. The resulting illumination or lack thereof is a downstream effect. This design logic ensures that the same switch can be used for any electrical device, from a lamp to a motor, with a universally understood command set, even if acquiring that understanding requires a minor, one-time conceptual calibration.