I’ve mentioned some of the changes in kinds of advances the players can discover before, but would like to give a fuller explanation now.
In the original design of the game, I hadn’t even come up with the word “advances” yet; the players could discover new “units.” I hadn’t thought of anything else. (This was not the only thing I hadn’t thought through, as my earlier posts make clear.) I had to make something up when players started submitting designs of things that were obviously not units.
In that first campaign, and for a long time after that, there were four basic categories of advances: units, improvements, general advances, and projectiles. That last, “projectiles,” also included any sort of explosive or bomb. There were three subcategories of improvements, based on what they could be added to: fortresses, units, or tiles. Tile improvements were usually things like roads or canals, though in modern-era and futuristic technological levels very large weapons and the like counted. Most other improvements could be equipped to either fortresses or units, with methods to improve logistical efficiency (nonsensical on a unit) or equipment to increase movement speed (useless for a fortress’s permanent garrison), for example, the rare exceptions. Later on, I added three new categories: objects, wonders, and wondrous objects. “Wonders” were basically massively expensive fortress or tile improvements that could usually only be built once per map. I invented “objects” as the category for the sizable number of things I had been filing under “projectiles” simply because they needed to be carried and transferable from unit to unit. “Wondrous objects” were objects that either couldn’t be built (I had thoughts of putting something like Tolkien’s palantir into a map) or were massively expensive one-offs, like wonders only portable.
Later on I revised the classification scheme slightly. There were still units, but many former fortress improvements (“fletcher,” I think, for instance) became units. Other fortress improvements and many tile improvements became “buildings.” Most unit improvements became “weapons,” while those that didn’t fit that category generally became general advances. Projectiles and wonders still survived as categories; I’m not sure about objects, wonders, and wondrous objects. The real trouble with this system was that “general advances” became the catch-all category rather than a narrow category for not-immediately-useful prerequisite advances like “fusion.” A vast number of “general advances” explained a technology and included phrases like “when discovered automatically equipped on all applicable units,” which is highly unfair to the players if there’s any even quasi-realistic economic model in place, and the economic model of Strategic Primer has been becoming more realistic with nearly every change to its design since it began.
The most recent revision, which I think I began in 2008, has finally eliminated the “units” category of advances. (A player still has “units,” but a unit is defined in terms of other advance types.) That category’s contents was split into three new categories: training (“Jobs”), equipment (“Implements”), and combinations thereof (“Suggested Unit Configurations”). All Weapons and most Buildings became (or, rather, are becoming; I haven’t finished the conversion process yet) Implements, as did (or will) most not-general-enough General Advances, though (alone of the previous system’s terms) that category survives. I had to improvise a new category recently in addition to those four: Domesticated Animals. And I still haven’t figured out what to do with what had been Projectiles. (Former Objects are of course Implements, but Implements are supposed to be basically permanent and relatively few, while Projectiles are transient and many.)