Monday, January 12, 2015

BU to HP

Part I

I've been building a theory over the past few weeks about hit points.  It is a sensitive subject, something people seem to get upset about.  However, I find as I develop and expand my game design, as a mechanic hit points tend to be somewhat mercurial, making it difficult to express to my players, in terms they can understand, how hit points work and what is happening when hit points are increased.

This post hopes to build a framework for these things - but I warn the reader, I'm going to discuss an idea that the average DM doesn't care about, has not or cannot conceive of, falling clearly under the heading of 'not fun.'  I'm going to take hit points apart in a manner more detailed than what most of you would ever consider.  This post is also going to be too long . . . so feel free to tune out now.

The term 'hit points' is vague.  I think it's far too familiar to for an initial deconstruction, so at the beginning of this post I'm going to avoid that reference.  Instead, I'd like to discuss the pure biological/physical construction of the body using a different measurement, biological units (BU).  These are meant to describe characteristics of origin, growth, reproduction and structure, relative to maintenance of the body and in no way affected by the skill of the body's user.  How the body is used, therefore, is not inherent in the number of BU the body has - only the body's capacity for sustaining and surviving damage, however that damage may occur.

I propose that an average 150 lb. to 210 lb. human body in top condition - in the best of health, at the point where physical shape and fitness are at their peak - would have a set number of BU.  Keep in mind that we are speaking of a body that has not trained, an activity that would suggest the acquisition of a skill.  I am merely speaking of a full-grown body lacking ailments or physical disabilities, that has been properly nourished and kept in a state of readiness to perform mechanical work (as physics defines the term).

Let's establish that number as a total of 12 BU, understanding that this number would indicate a body at the height of its status, so that the removal of all the body's BU would mean death.

Just to be weird, however, suppose that instead of rating 'death' as occurring at 0 BU, we establish the bottom of the scale at -3 BU.  Believe me, mathematics doesn't care where we start counting.  We can therefore use the balance of BU on either side of the number zero as an easy way to keep account of what is happening to the body as BU is removed by damage.  Thus the figure below indicates the spread of BU between -3 and 8:

Feel free to count the columns.  As we move off the left end of the scale, death occurs (at -4 BU). Alternatively, it is impossible to move above the right end of the scale.  It is not possible to be more alive than alive.  Therefore, 8 BU is the maximum number of BU that a human of such-and-such a mass can possess.  Remember, BU are not hit points!

The benefit of beginning the scale at -3 is how this allows us to divide vitality into three categories:  a) illness, in which the body's BU is less than zero; b) vigorous, in which the body's BU is above zero; and c) sapped, or exhausted, in which the body's BU is equal to zero.  Sapped does not indicate that the body is ailing, only that it has reached the point where the body is strained.  Further effort is possible, but it would probably result in the body becoming ill.

Glancing at the left end of the scale, we can judge the medical state of the body in three levels: critical (-3), serious (-2) and subdued (-1).  A critical condition, where 1 BU separates the body from death, could be described as intense weakness, an inability to rise, tend to one's self, drifting in and out of consciousness (more out than in) and probability of not being fully aware when awake.  A serious condition could be described as moderate weakness, some mobility but requiring assistance and periods of lucidity separated by long periods of sleep (or fitful hours of sleep spread throughout the 24 hour day).  Finally, a subdued condition would require plenty of bedrest and considerably reduced energy, but the ability to attend to one's self.

Looking at the vigorous end of the chart, it is presumed that, in all but the chronically ill, a healthy body will have a positive number of BUs.  This does not mean that every body would be vital enough to possess 8 BUs above zero!  The number of actual BUs possessed must depend upon the condition in which the body is kept, complimented by the condition the body possessed at birth.  We can, if we like, extrapolate the 8 points of BU above zero as a composite of different elements that combine to form vitality.

I propose the following:

  • Activity, normal employment of the body's capacity for the expenditure of energy.
  • Depreciation, devaluation of the body accumulated due to use
  • Happiness, the positivity and mental attitude that encourages vigor 
  • Health, the soundness of the body, freeness from chronic disease or ailment
  • Heredity, the transmission of genetic characteristics from parents to offspring
  • Initiative, a readiness and ability to initiate action
  • Maturity, the degree of physical development increasing or decreasing towards/from peak
  • Nourishment, food and sustenance consumed throughout the body's lifetime
Others may suggest additional possibilities; some may contend that one or all of them are inherent in the individual's abilities scores.  I don't think that matters.  I do not contend that BUs are measured contrary of constitution, intelligence, strength or dexterity - only that they are measured contrary to training or skill.  The elements above do not depend for their existence upon training.  This does not say that a given uneducated individual has a high level of happiness or initiative (those vital composite parts most suggestive of mind rather than body), only that there is some measurable existence of either prior to training.  The same is true of the remaining six composite parts of vitality.

This is key.  There is some measure of each, which combined produce the number of BUs a body (mind included) possesses above zero.  The combination need not be the same from body to body - this body may be high in heredity, nourishment and maturity, while another may be high in happiness, health and activity.  We might, to determine the balance, roll a d8 for each of the 8 elements, dividing the total by 8 to achieve an average.  Alternately, we might suppose that certain composite parts of vitality were universally poor for an entire region - examples would include the degree of expected nourishment in certain parts of Africa, the depreciation of an entire country due to continuous war or enslavement, comparative initiative between regions of abundance and scarcity, etcetera.  The resulting average number of BUs across a population might reasonably be expected to be less than, say, 4.5 (8 x d8 /8).

Part II

Very well, how might we derive a concept of hit points from the above framework of biological units?

Let us consider basic combat training, concentrating specifically upon improving the physical and mental acuity of the subject.  Obviously, in choosing a candidate for training, we want someone with the greatest number of BUs possible.  However, it is unlikely that any of the candidates we find will have a BU higher than 6.5 (without doing the math, the reader may take my word for it that rolling more than 52 on 8d8 is unlikely - though the reader is invited to try).  Still, we know that through training, a relatively ordinary body between the ages of 16 and 24 can be improved - therefore we know that in those candidates, at least one 8th of the body's vitality can be created where it does not formerly exist.

The same can be said of the body's activity, certainly.  Happiness and initiative can be redirected or enabled.  Depreciation that has occurred in a young body can probably be overcome through expanding lung and heart capacity.  Nourishment can be provided.  Finally, both health and heredity can be chosen for - and if the choice proves inadequate, the candidate can be dumped mid-way through training or retained even if the final results are somewhat less than ideal.

This would mean that, at the end of basic training, we are improving each candidate's BU through rigorous training from an average of 4.5 to an average of somewhere between 6 and 8.

We can view the result to be "combat-trained" recruits - able to recognize what a weapon is and to hold it, but possessing no special ability in the use of a weapon or moving easily in armour.  Take note that these recruits would also lack any sort of combat experience, at all.  Their entire potential is based upon their physical capacity alone.

As active combatants in a D&D world, they would have - yes, you guessed it - 6 to 8 hit points.  To this I am adding the supposition that these same combatants (indeed any person) would not die at zero hit points.  This would be a first-time proposal for me.  Yet the increased number of followers employed by my parties has made me consider the importance of allowing a negative/illness (comparative to severely damaged) buffer between exhaustion and death.  I'll begin testing the proposal in months to come.

Given this system of BUs regulating the maximum number of hit points for combat-trained recruits, however, how does it happen that its possible to have hit point totals that are much higher? I'll just restate my point from earlier: 8 BU is the maximum number of BU that a human of such-and-such a mass can possess.  

Before we get to that, compare the damage done by a weapon, say a dagger, against the number of BU that the body possesses (no, not the number of hit points - keep up).  Let's say that the effectiveness of the dagger is based on chance, so that as I turn to attack you with the dagger, I may nick your arm, cut a deep slash across your belly, skid the dagger along your ribs or plunge the dagger directly into your chest. These different attacks might reduce your BU, comparatively,  1, 2, 3 or 4 points.

Imagine that any strike with the dagger that deprives a defender of half the defender's BU above zero causes a wound.  I wrote some content about wounds in the link that describes what happens when 11 hp damage is done to a creature.  Since we are talking BU and not hp, we can use the same rules to apply to this circumstance.  A tough body with 6 BU above zero is struck with a dagger, causing 3 BU in damage.  This may not be enough to immediately kill the defender, but the defender will lose 1 BU every following round (which in my system is 12 seconds).  Reduced to 3 BU, we know that it will take 7 rounds for the defender to be reduced to -4 BU, or death.  That is a total of 84 seconds, less than a minute and a half.

Observe very closely the last point in the link on wounding, which itself links to this page.  The bleeding defender with 3 BU will be stunned every round until death occurs - unless this death is staved off by an ally or bystander.

This means that a dagger could kill an ordinary defender with as many as 8 BU - who would be stunned by the original hit and then stunned every round thereafter - even though the dagger can only cause 1d4 points of damage.

From this, it sounds like I'm saying that BU are equal to hit points.  I'm not.  I am saying that where no experience has been gained, BU and hit points are coincidentally equal in value.

So let's talk about experience.

Part III

According to wikipedia, Experience "is the knowledge or mastery of an event or subject gained through involvement in or exposure to it." [bold face added by me].  It is from this that I argue an individual cannot be talked into an improved combat ability - this ability is gained through immersion and the development of a relationship with an enemy attempting to use a weapon to kill you. Skill is acquired through repetition and experimentation - holding the weapon, wearing the armor, growing comfortable, obtaining the necessary callouses and balance through endless physical practice and training.

Eventually, however, to level means more than growing comfortable with the mechanics of war - it means growing to the point where one is able to function when swimming in a maelstrom of intoxicating adrenaline and hormonal signals coming from a body made terrified and insane by the possibility of immediate death, the smell and taste of blood, pain and a ludicrous dopamine high that will result from success.  In the end, mechanics will fail in the face of chemistry.  The survivor in that chaos is not the one who can rationally piece together how to turn the sword of the enemy or physically endure the dagger's blow.  The survivor is the one who does not get hit in a way that causes a critical wound.

Imagine, then, a character that has no combat training - let's say, a mage.  Because we are speaking of a character who's power derives from mental development rather than the physical, we may assume the mage has an average of 4.5 BU.  In my system, I account for this by calling it mass and assigning 1d8 hit points to the mage if he or she possesses the appropriate weight (I could write a couple of paragraphs about BU and its relationship to a mass greater than the average human described here, but let's leave that on the shelf and move forward).

On top of this, we already know that the mage has an additional 1d4 hit points.  This, of course, is the original total number of hit points a mage is supposed to start with in traditional D&D, but in the end I've had to ditch this as a viable number of hit points.  Granted, in the system I've developed, there is still a 1 in 32 chance that a mage without any constitution bonus will have only 5 hp, but c'est la vie.  I'm digressing here.

Where do these additional hit points come from?  Traditionally, we view them as added onto the existing mass, perhaps with the suggestion that the initial damage done to the character would be these extra 'skill-type' hit points, so that the body is only attacked when the character is reduced to 8 hit points or less . . . but I consider that argument invalid.  I am here to propose another.

Suppose we imagine a mage, Erick, who rolls a 4 for his mass and a 3 for his d4 leveled hit points, making a total of 7.  Since I use the rule where a leveled character doesn't die until -10 hp, this gives Erick a considerably wider range of hit points (17) than Erick's BU - which, because Erick has 4 BU above zero, is a total of 8 points stretching from -3 BU to 4.  I sure hope the reader is keeping up.

Let's put up a new chart, comparing Erick's BU to Erick's hit points:

The theory is simply this: that as a player grows in experience, the damage done by the weapon, applied to the creature's BU, is lessened by the player's experience (and gained hit points).  Where the creature's BU would be expended in an unleveled character after suffering only 4 damage, the same amount of damage caused against Erick only reduces Erick's BU by 2 points.

Were I to use the "half BUs causes a wound" proposal, either 3 or 4 damage would still wound Erick (in my game as it stands, it already stuns him) - but this is better than the 2 required if he had no training at all as a mage.  Given another level, it would be unlikely that a dagger hit would wound him - thus reducing his chances of being killed by a dagger.

How?  Because with experience, Erick has learned to shift and turn his body so that the 'dagger in the chest' result won't happen until Erick's overall BU has been spent (ie., reduced to his last hit points).  It means that the 1d4 damage done by the dagger no longer has the four possible results described above, but something closer to "nicks arm," "grazes face," "produces furrow in shoulder" and "cuts deep into side."  The importance of the d4 damage the dagger does is relative to the opponent the dagger is used against.

The same applies to the severity of injuries/ailments that accumulate on the left end of the scale.  Experienced characters take better care of themselves, monitor themselves to a greater degree, make better use of their existing constitution and strength, endure pain more easily and are less likely to do something that stupid that would cause an injury to become worse.  The untrained, ignorant body may have a constitution of 15, but that constitution in the hands of a character with three levels of experience is much better exploited.

(This does go against certain ideas I had about ability stats that were posted years ago on this blog, but better ideas will gradually replace weaker proposals).

If you have made it this far, you may be wondering why I should go to this length to detail a fairly simple notion.  How has all this made an important difference to the substantial nature of hit points?

I believe that the theory builds an important construct between the nature of hit points and the nature of real injury, while satisfactorily keeping them apart.  For example, it means that when resting to regain health, we should adjust the creature's BU and not the creature's actual hit points.  When poison enters the body, the poison should attack the creature's BU.  The same ideal can be applied to injuries that hit points cannot account for, such as broken arms or ribs, providing a structure for the healing of these things that is set apart from the creature's level or total hit points.

Having created the supposition, there are directions in which the game can be structured more rationally - while remaining simple to understand and immensely playable - where before the limited restrictions of hit points lost/hit points restored allowed for little development where elements of injury and being alive were concerned.

It is a change in thinking, not a change in the original game principles.  Hit points (with the exception of my possibly increasing my wounding rules) remain unaltered by the change, so that no changes need to be made to all other aspects of the game already incorporating hit points.  It is added structure without needing to tear everything down and start again.  For me, this is the best sort of game redesign there is.


Arduin said...

That second chart made the post. Very cool to think about, and the possibilities it creates in terms of potential in-game effects is amazing.

Diseases or poisons could actually be made to deal damage directly to BU, making them potentially debilitating/lethal even to higher-level characters.

Imagine a weary warrior-king forced from his sickbed to take up arms against an invading force, stuck with a fraction of his hp at most! So cool.

This is the stuff that keeps me reading, bravo.

William Jones said...

This is really good, and distils something that has been on my mind for a while into a really workable system. I had experimented with not giving players extra HP as they levelled but instead reducing damage based on their level previously, and while it was worked into a usable system in the end, it did not have the simplicity or elegance that your way has the potential to have, and the way your system naturally expands to allow for attacks directly to the BU is nice and neat!

I know you're not a huge fan of 5th edition, I agree with you, but for me, there is a lot to like in it too and I am determined to house rule it into submission and this is definitely going to be the basis on how I handle heath and HP(though I am thinking over using CON actually as the BU, a rejiggle of your numbers), so thanks! Now all I have to do is work out how to present it neatly and intuitively on a character sheet!

Ozzie Pippenger said...

This looks like a good system. I'm not really playing these days, but it feels nice to finally see an explanation of hit points that makes some logical sense, so I just wanted to say I think you're doing good work here.

Matt said...

This is brilliant.

If I understand correctly Erick's BU and his HP are linked. If Erick takes 4 points of damage reducing his HP from 7 to 3, his BU will similarly be reduced to 2 (and he will be wounded, which will cause him to lose 1 BU per round hereafter.)

If he is effected by something that directly damages his BU, dropping it from 4 to 2, his HP will be reduced to 4. (And he is still wounded.)

How does this translate to higher HP values? If Erick is higher level, and has 32 hit points how are those assigned across his BU? Are they just evenly distributed?

Also, it seems by the wounding rules that once you are wounded, whether you are level 1 or level 10 you are bleeding out at the same rate. I assume this is working as intended, but I can imagine my players' faces as they hemorrhage 8 HP per round.

If I can add my own thoughts: Inclimate Weather. If the party finds themselves travelling in the constant rain, or through colder winds than they prepared for, a loss of 1 BU would be devastating for the poorly conditioned mage, but pretty manageable for the well travelled Fighter.

Alexis Smolensk said...


Yes, as hit points are accumulated, they would be evenly distributed.

The same rate for wounding is intended - as you level, the wound has less impact upon your action and effectiveness in combat.

Discord said...

This system is pretty amazing. I especially relish the fact that you've put more time, effort and RESEARCH into the problem than the original designers did. Major kudos!

I notice in the post that 12 BUs are listed as the maximum for a human of such-and-such mass. Do you plan to expand this for: different human masses, different masses for different humanoid races (human versus dwarf) and different non-humanoid races (horses, dragons, etc.)?

Matt said...

It also just occurred to me that you could use BU to give situational bonuses and penalties to a character, if that was your bag.

If we wanted to use low BU to simulate being unfit to fight, we could say that any character at 1 or 2 BU suffers a penalty to attack, or to armor class. Conversely, a character at 7 or 8 BU might gain similar bonuses.

I doubt that you want to use the system that way, but it is very exciting how many uses this scale has. I will definitely be using this.

Alexis Smolensk said...

Yes, Discord.

Humans and demi-humans fall into the 1 HD category as far as creatures go. Everything above would dovetail with my own wider mass per hit die rule.

Most dumb creatures (anything without trained skills) will fit into a 1 BU = 1 HP framework - but dragons would have extra hit points for mage training, rakshasa would have extra hit points for clerical training, a hill giant army commander would have extra hit points for fighter training and so on.

Alexis Smolensk said...


That makes me think of the party encountering orcs patrols outside their lairs. I've done all this math to indicate that these orcs ought to have more health than average orcs, like 7 or 8 BUs, rather than 1-8 like the book suggests.

Wait, wait, I think I wrote about this once before! Was it here?

Matt said...

Exactly! My thought was to translate that to other mechanics. The person at 1 BU might take a -2 penalty to attack and AC either because they are just completely worthless in a fight, or because they have beaten into being completely worthless in a fight.

I don't think I'm the only one who saw this post as a natural expansion of those HP posts. I've been so excited about commenting because I loved the insight those posts had. They got me thinking about transparency with my players, and how much information I could impart by just sharing HP values.

Scarbrow said...

If I understand correctly, you'll spread the positive hit points over the "healthy" positive BU's (>0) and the (leveled characters') fixed nine negative hit points over the (fixed) three negative BU's (<0), with 0 BU always corresponding to 0 HP. So negative hit points will always translate to negative BU's as 3:1, but as hit points increase, the HP:BU ratio will grow from 1:1 to 2:1, 3:1 and so on. This means all "wounded and stunned" creatures will die at the same moment and at the same rate, consistent with the hypothesis of BU's being an expression of pure physical fitness. You cannot train to not die and you cannot train to bleed less. Have I understood it right?

Then, concerning wounds, the advantage of higher-leveled characters is not that they are more resistant to wounds, but that they are harder to wound (need to lose more HP to lose half their BU) owing to skill and training.

I have, however, a question. You say in the text that the wound would happen when losing "half the defender's BU above zero". Would that be total BU over 0 (which seems consistent with the fixed scale of 11HP shown on wounds wiki page), or current BU over 0 ("at the time the damage was done", as suggested by the "stunning" wiki page). I suppose it's the former, but I'd like to make sure.

I'm also interested in the extension of this system to greater masses, as you hinted you would treat another time. Would you extend the negative range too, or just the positives? With time-to-death-from-0-HP depending on this, I think I would. How about you?

Thank you again for a clear example of how to design and explain mechanics.

Alexis Smolensk said...


Your first paragraph more or less has it right, except that you Can train to bleed less. A sword cut that would hit directly and cut open a mere soldier would only tear the skin on a master at arms because of how the latter would shift to avoid the direct hit. Comparatively, the master would bleed less because the wounds the master received would be less deep.

According to the post above, the 'wound' would be half the defender's BU above zero. However, I added the content above wounds for this post in order to bring home the difference between BU and hit points. I actually run my wounds according to these rules on my wiki - which makes every hp damage of a certain amount count as a wound, while enabling persons with higher levels to survive wounds better.