Chainmail Fantasy -- Here's how it begins in Chainmail:
Phantasmal Forces: The creation of the apparition of a unit or creature for four turns, maxi-duration. (Complexity 2) [CM, p. 31]Wow, we do like things to be short, don't we? The interesting thing here, compared to later editions, is that the spell simply creates a temporary unit in your man-to-man skirmish game. ("Forces", as in "any organized group of soldiers, sailors, etc.", per Webster's.) Presumably the unit is fully functional the same as any other (re: move, attacks, and damage), but merely temporary? Apparently you're conjuring ghost-like warriors to fight for you, something like a proto-monster summoning spell, or the "Shadow Host" from the end of Lord of the Rings. I thought it was really interesting to realize where the name came from originally.
Original D&D -- Next let's look at the spell list in Original D&D, Volume 1:
Phantasmal Forces: The creation of vivid illusions of nearly anything the user envisions (a projected mental image so to speak). As long as the caster concentrates on the spell, the illusion will continue unless touched by some living creature, so there is no limit on duration, per se. Damage caused to viewers of a Phantasmal Force will be real if the illusion is believed to be real. Range: 24". [Vol-1, p. 24]Now the spell has become a general-purpose illusion spell (2nd-level). It's still called "phantasmal forces", plural. The effect is also cited by the wand of illusion in Vol-2. While illusory, it can still cause real damage (in the tradition of Chainmail fighting forces, I assume?) But now, a major contradiction: The illusion does damage if believed to be real, yet it disappears when touched by any living creature. Personally, I'm having a hard time imagining any circumstances where the illusion could cause damage without touching the victim in question (and thereby disappearing and disrupting the effect, right?)
Advanced D&D 1E -- Now consider the AD&D Player's Handbook:
Phantasmal Force (Illusion/Phantasm): ... When this spell is cast, the magic-user creates a visual illusion which will affect all believing creatures which view the phantasmal force, even to the extent of suffering damage from phantasmal missiles or from falling into an illusory pit full of sharp spikes. Note that audial illusion is not a component of the spell. The illusion lasts until struck by an opponent - unless the spell caster causes the illusion to react appropriately - or until the magic-user ceases concentration upon the spell (due to desire, moving, or successful attack which causes damage). Creatures which disbelieve the phantasmal force gain a saving throw versus the spell, and if they succeed, they see it for what it is and add +4 to associates’ saving throws if this knowledge can be communicated effectively. Creatures not observing the spell effect are immune until they view it. The spell can create the illusion of any object, or creature, or force, as long as it is within the boundaries of the spell’s area of effect. This area can move within the limits of the range. The material component of the spell is a bit of fleece. [PHB, p. 75]At this point, the spell is called "phantasmal force" in the singular, and it's been bumped up to 3rd-level. There's generally a lot more detail here (the general-purpose is expanded into "any object, or creature, or force", the "visual" but not "audial" component is specified, etc.) It still does actual damage, and the spell can be maintained after contact due to the "unless the spell caster causes the illusion to react appropriately" clause (and I presume that any spellcaster would do so by default). There's a small bit of addendum in the DMG (p. 45): "The magic-user must know of and understand the force/creature he/she is making an illusion of."
Now, there's a number of things that trouble me about this version (which may be the one most familiar to many of us). One is the possibility of falling into illusory pits: Apparently the spell is so strong that the viewers can go into a hallucinatory state and not even know what their physical location is. (What is seen by outsiders, the victim flailing prone on the floor? Is the victim unable to see the presumably occluded caster? How does the victim return mentally to their actual real-world location? Does stepping onto an illusory bridge cause one & one's associates to mentally see themselves as walking forward when they're actually falling to their doom?)
More importantly, though, is the mother-of-all-complications, that line that says, "Creatures which disbelieve the phantasmal force gain a saving throw versus the spell", resulting in fifty thousand AD&D players shouting "I disbelieve!!" at every encounter for the next decade, on the off chance that it was an illusion and they could save against it. What other D&D spell requires a specific technical meta-game action like this before a save is allowed? And how does the DM adjudicate this for monsters?
This difficulty generated a few different articles in Dragon magazines of the era, which I'll briefly survey here. In Dragon #43, Philip Meyers ("Now you see it... but is it really there?", Nov-1980) presents a system for deciding when monsters will opt to "disbelieve". Illusions are ranked by the DM on a 6-point scale as to believability, then cross-referenced with the Intelligence score and some other modifiers, and percentile dice are rolled; success indicates the need for a follow-up saving throw. In Dragon #66, Tom Armstrong ("Is it really real?", Oct-1982) makes a case that the damage potential is realistic in that it simulates a "shock" effect (i.e., acute stress disorder, with reference to a medical book from 1919 by Virgil H. Moon, and news stories from 1979), whereas illusory healing could not have the same effect (exception: illusory damage could be recorded separately and then healed with an illusory cleric); and he recommends abandoning the Meyers method in favor of a single saving throw for monsters, "secretly modified by the DM if the situation warrants it." Meanwhile, a sidebar by Quinn & Young ("Familiarity factor prevents illusionists from stealing the show") also recommends a single-saving throw method, with specific bonuses based on spell level, Intelligence, and familiarity of the actual phenomena to the caster. In short, many of us struggled with both the spell's damage-dealing capacity, and the devilish "creatures which disbelieve" clause from the PHB.
Advanced D&D 2E -- In 2nd Edition the spell drops all the way down to 1st-level, but the effect is (as usual) mostly just copied from the preceding:
Phantasmal Force (Illusion/Phantasm): ... This spell creates the illusion of any object, creature, or force, as long as it is within the boundaries of the spell's area of effect. The illusion is visual and affects all believing creatures (undead are immune) that view it. It does not create sound, smell, or temperature. Effects that depend on these senses usually fail. The illusion lasts until struck by an opponent--unless the spellcaster causes the illusion to react appropriately--or until the wizard ceases concentration upon the spell (due to desire, moving, or a successful attack that causes damage). Saving throws for illusions are explained under "Illusions" in Chapter 7: Magic and under "Adjudicating Illusions" at the beginning of Appendix 2. Creatures that disbelieve the illusion see it for what it is and add +4 to associates' saving throws if this knowledge can be communicated effectively. Creatures believing the illusion are subject to its effects (again, as explained in Chapter 7). The illusionary effect can be moved by the caster within the limits of the area of effect. The DM has to rule on the effectiveness of this spell; detailed guidelines are outlined in Chapter 7: Magic and under "Adjudicating Illusions" at the beginning of Appendix 2. The material component of the spell is a bit of fleece. [2E PHB]So again, this is mostly the same effect, but now at 1st-level. What of the Chapter 7 reference? Well, the text for the effect now explodes into a whole partial-chapter, running some 20 paragraphs long -- plus another 12 paragraphs in Appendix 2. In general, it's the standard 2E vagary of the, "You could consider this! Or consider this! Or consider this!" variety, without any concrete game-mechanics to back them up. A few exceptions: The "actively disbelieve" requirement is maintained before a save is allowed (DM fiat for monsters). They don't cause "real" damage, but do cause "illusory" damage which is recorded separately by the DM; when 0 hp is reached, a system-shock roll is made to determine survival. Characters can still mentally fall into an illusory pit or "lean" against an illusory wall, but if pushed externally then they'll be surprised to find themselves falling through it (uh, what?)
Dungeons & Dragons 3E -- Now in 3E, there is no longer any spell by the name "phantasmal force", but there are similar illusory spells at both 1st and 2nd level (and more at higher levels, too):
Silent Image: Illusion (Figment)... This spell creates the visual illusion of an object, creature, or force, as visualized by the character. The illusion does not create sound, smell, texture, or temperature. The character can move the image within the limits of the size of the effect.Silent image is very similar to 2E's phantasmal force, with the 2nd-level minor image differing only with the addition of some non-speech, minor sounds. But overall, the spell descriptions here are radically shortened, with the heavy lifting all moved off to a special chapter section on illusions/figments (following the lead of 2E). In that section, the biggest change is that they simply "cannot cause damage to objects or creatures... these spells are useful for confounding or delaying foes, but useless for attacking them directly" [3E PHB, p. 158]. You still need to "disbelieve" before a saving throw is allowed, but this doesn't need to be a proactive decision: "interaction" suffices, and "faced with incontrovertible proof" (like falling through an illusory wall), one auto-saves against the effect.
Minor Image: Illusion (Figment) ... This spell creates the visual illusion of an object, creature, or force, as visualized by the character. The spell includes some minor sounds but not understandable speech. The illusion does not create smell, texture, or temperature. The character can move the image within the limits of the size of the effect. [SRD]
Holmes Basic D&D -- Now we'll check in on the parallel line of Basic D&D. In the Holmes blue-book we see this:
Phantasmal Forces -- Level 2; Range: 240 feet; Duration: Infinite. Creation of vivid illusions of nearly anything the user envisions (a kind of projected mental image). The illusion persists as long as the caster concentrates on it unless it is touched by a living creature. Damage caused by the illusion will be real if the illusion is believed to be real. Note the illusion is visual and not auditory. [Holmes, p. 16]So this is pretty much a copy-and-paste operation on the spell from Original D&D, with some minor re-ordering of the sentence structures. The name is still "forces" plural, the subject matter is still totally open-ended, and damage inflicted is real. The "no audio" which we otherwise first saw in 1E AD&D has been ported in here, as well.
Moldvay Basic D&D -- Now here's Tom Moldvay's take on the issue (again, 2nd level):
Phantasmal Force -- Range: 240'; Duration: concentration. This spell creates or changes appearances within the area of the spell effect: up to a 20' × 20' × 20' cube. The caster should create an illusion of something he or she has seen. If not, the DM should give a bonus to saving throws against this spell's attacks. If the caster does not use the spell to attack, the illusion will disappear if it is touched. If the spell is used to "create" a monster, it will have an Armor Class of 9 and will disappear if hit. If the spell is used as an attack (a false magic missile, a collapsing wall, etc.), the attack will not affect a victim who saves vs. Spells. If the caster moves or is affected by any attack in combat, the illusion will disappear and not return. This spell never inflicts any real damage. Those "killed" will pass out, those "turned to stone" will be paralyzed, and so forth. These effects will wear off in 1-4 (1d4) turns. [Moldvay p. B17-B18]So once again, we see Moldvay here doing yeoman's work in detecting the trouble spots of classic D&D and making very legitimate, pretty elegant fixes where needed. Apparently he's the first one to switch off the "real damage" component of the spell, to give specific mechanics to hitting and disrupting the illusion (AC9, any hit dispels), and to crack down on the concentration of magic-users using the spell. This is pretty good stuff, and it's unique to his branch of the game; it was maintained unchanged throughout the later Mentzer D&D and Allston Rules Cyclopedia editions.
Summary -- Phantasmal force(s) was one of the most problematic spells in D&D editions 0-2. In fact, it ping-ponged around different levels more than any other spell in the game (initially 2nd, then 3rd, then 1st), as designers struggled with exactly how powerful the effect was supposed to be (and depending greatly on DM adjudication). Major problem (1) is that the effect was completely open-ended, limited only by the player-caster's imagination, and could cause actual damage based on that effect. In fact: a permitted example in the 2E text is for the (1st-level) spell to create a ceiling cave-in for an automatic kill. (Holy crap!) Or, you could simulate a meteor swarm, an earthquake, gating in Orcus, or whatever else you like, for full actual effect. (2) Would be the fact that gauging "believability" on the part of the DM is practically impossible in the context of a fantasy world. For example, all of the previously suggested catastrophes are, indeed, actual permitted attack forms in AD&D. (3) Is the need for the "disbelieve!" request, which is a narrow meta-game technical demand on the players (consider that new players won't naturally know about this possibility?), and a critical piece of DM fiat for any monsters.
Unlike many other famous game effects, the fundamental tension here arose in the switch from Chainmail to original Dungeons & Dragons, where the spell changed from a ghostly fighting force to an all-purpose illusory image. The built-in contradiction between "ends if touched" and "damage is real if believed" was never fully resolved. Personally, I think that any of the following would have been reasonable mechanics by themselves: (1) ghostly fighters with fixed stats, (2) a "shocking" effect with fixed damage, or (3) a visual mirage with no capacity to damage. But the open-ended effect, real-but-not-real damage, "I disbelieve!", and may-or-may-not end on contact, was something of a continuing open sore throughout the AD&D era.
[Illustration by CapCat Ragu under CC2.]