Is there a missing skill in the PHB?

Question

In the player's Handbook version 3.5 the only Engineering type skill listed is attached to Architecture, which implies that it's the form of engineering used to design things such as suspension bridges.

Having said that, things such as Iron Golems, Dwarven Tunnellers, Gnomish contraptions, and assorted mechanical devices exist, Which simultaneously implies that there should also be a skill governing the type of engineering involved in designing machines, Which I have always been led to believe is not the same type of engineering as the one involving the creation of large structures such as the Aforementioned bridges.

So I'm either mistaken in this assumption, the person who wrote the skills in the Player's Handbook book was mistaken in believing the 2 forms of Engineering are the same, or there's a missing skill in the PHB. Which is it?

Do I simply need to create a new skill to govern the designing of machinery?

Answer 1

Knowing stuff about machinery goes under Knowledge (architecture & engineering). Yes, that means the one skill covers some fairly disparate stuff, but that’s the nature of a game—it has to simplify reality in order to be playable. Many of the skills in the game are multi-purpose, and not all of those purposes are necessarily trained for in the same ways—which means it’s plausible to be good at one and not the other in real life, but in the game that’s not an option. This is a trade-off, a very intentional one, to keep the complexity of the skill system down.

And it wasn’t enough. Characters, even entire parties, have nowhere near enough skill points to actually cover all the skills in the game. Most parties won’t have anyone with any ranks in Knowledge (architecture & engineering). It doesn’t come up enough to be worth it, not when there are so many other, more important skills to cover. Many tables use houserules to combine skills further, even, just to make things more manageable. Pathfinder, a 3.5e spin-off, even made that “official” (though in my opinion they didn’t go far enough).

And the opposite solution—more skill points—isn’t popular because despite the simplification that went into the skills we have, assigning skill points is still much too complicated—another thing Pathfinder simplified further. And we can look beyond 3.5e and its near-clone spin-off here: 4e and 5e eliminated skill points entirely, changing things to just being “proficient” or not in a skill—and drastically shortening the list of skills, beyond even Pathfinder.

Now then, considering that, it makes more sense that Knowledge (architecture & engineering) covers a rather broad swath of knowledge, which is precisely what it does.

Beyond knowing about mechanics, a character might also need to use Craft to actually build a machine. The Craft skill is kind of nebulously defined, so this would be left up to the DM. Certainly, mechanical traps require Craft (trapmaking) to make.

But that still doesn’t actually really address most of your concerns. That’s because for the most part, the world of D&D does not have complicated machines. Maybe Renaissance-era mechanics, but even then we aren’t really talking Da Vinci here. A bridge—and all the associated scaffolding, pulleys, and so on—might well be the most complicated engineering that anyone’s doing in the world.

Which brings us to your iron golems—those aren’t mechanical. Golems are sculptures, brought to life with magic:

An iron golem’s body is sculpted from 5,000 pounds of pure iron, smelted with rare tinctures and admixtures costing at least 10,000 gp. Assembling the body requires a DC 20 Craft (armorsmithing) check or a DC 20 Craft (weaponsmithing) check.

No mechanics involved here, so the crafter doesn’t need to know anything about them.

Instead, the crafter needs magic, specifically:

CL 16th; Craft Construct, cloudkill, geas/quest, limited wish, caster must be at least 16th level; Price 150,000 gp; Cost 80,000 gp + 5,600 XP.

High level, a specific feat, and three mid-to-high-level spells.

And knowing things about iron golems—about all constructs—isn’t Knowledge (architecture & engineering)! It’s Knowledge (arcana). Because you have to know about magic to understand them, because the magic is the real thing making them possible.

And that’s true of basically everything that seems like a complicated mechanism—they are substituting their magic for our superior knowledge of mechanisms.

So Knowledge (architecture & engineering) covers perhaps less than you think it does—because there’s simply less to know about engineering in D&D.

Answer 2

Aside from KRyan's valid points, it may be that in the early days of the core rules, this was some lingering influence from 2nd ed. Wizards had just acquired D&D from TSR, and when you look at it closely, the architecture and engineering knowledge seems to emphasize the "dungeons" in Dungeons and Dragons, and could conceivably play a big role. But a quick scrape of some of the material showed that they just didn't focus much on it when they started producing supplements and other materials, most likely because it's not obvious that you need it compared to the other knowledges. Of the many things you could know in 3.5, which would help solve your problems more: monsters/magic/gods, or building & systems structure?

The basic breakdown of the knowledge skill is

Architecture and engineering (buildings, aqueducts, bridges, fortifications)

The skill is a prerequisite for only 1 feat (as far as I could quickly find), Trap Engineer, which requires only 1 rank in the skill and whose benefit is:

You know the styles of famous dungeon architects or recognize their influences. After finding or setting off a trap in a dungeon, you gain a +2 bonus on future Search checks and Disable Device checks to find or disarm traps in that same dungeon. You also gain a +4 bonus on Reflex saves to avoid traps in that dungeon, and a +4 dodge bonus to Armor Class against attacks made by traps in that dungeon.

This kind of stuff reminds me of playing the old DOS games like Eye of the Beholder. But Wizards introduced so many mechanics from 2nd ed to 3.5 that characters ended up with more vulnerabilities that demanded points in other skills, and so this one kind of quietly fell into the background.

That being said, I think the intention of the skill was to encompass anything in the realm of "structural design", meaning any kind of (potentially mechanical) structure, and perhaps they thought "architecture and engineering" drove the point home better. For our campaign, it seemed like a no-brainer that this was the case. We had and are currently having an application of this skill in the game. One was a crazy gnome trap engineer that designed a whole lair for a dragon (knowing architecture may have helped us to identify the most likely spots for traps, etc). The ongoing one is an impressive ship that we got from a dragon who played some game amongst dragons on the prime material. We've gotta go find someone who has the requisite knowledge in architecture and engineering because this ship's inner workings are intense and complex.

Ultimately though as both a DM and a player I think it's great that it worked out this way in the game. What kind of adventurer would take that (see my question in the opening paragraph)? As a dungeon master, you'd really have to emphasize ways it could be useful to your players, otherwise they'd never take it, and even if you do emphasize it, they still probably won't! It could possibly be used as a means of navigating a dungeon faster (ex. a successful knowledge check can give the player a hunch as to where the most likely trap or secret door spots in a dungeon room are, if the players would normally be pressed for time) or perhaps something to the effect of "understanding where the upper level in the dungeon should be".