The dominant species on this alien planet are sapient, somewhat monstrous bipedal creatures. They possess no eyes at all, are completely blind, and have no concept of vision.

Other senses are as follows:

  • Touch: Their tactile senses are equivalent to a human's.
  • Hearing: They have sophisticated hearing organs slightly more powerful and capable of more nuance than human ears, especially underwater.
  • Smell & Taste: These senses are incredibly powerful and are their primary method of information-gathering. Their entire "face" opens into a fearsome maw (actually a combination mouth/nose orifice) through which they can rapidly sort out detailed information from particles in the air, in a manner akin to the flehmen response, only turned up to 11. They can also derive information underwater by filtering through chemicals in the water (as fish do), without drowning.

For all intents and purposes, the planet is oceanic, with huge diversity of sea-life, and most landmasses having a tropical biome. This species feeds entirely on fruit, vegetables, and seafood.

Civilization is at a tier 6 level, although this answer notes:

. . . the question of discovering mining, chemistry, medicine, etc. is much harder if not impossible if everyone is blind.

So mining, metalworking, and by extension, coin minting is likely to be underdeveloped at best, and nonexistant at worst, unless some condition reasonably exists that could outweigh the developmental hindrance of being blind. (I'm hesitant to just handwave it.)

Under these conditions, what would be a reasonable, reliable form of currency?

Paper notes would be out, as they're primarily vision-based currency. Coins could work, but, as stated above, I'm not sure if their development could be reasonably justified. I've also considered something like shells or coral, but they seem like they'd be too fragile for everyday use.

In summary, the currency needs to be:

  • Reasonably obtainable, but not overabundant
  • Portable
  • Waterproof (Bonus points if it's buoyant, though that's not a necessity)
  • Durable enough for everyday use
  • Be reliably distinguishable without sight
  • Have enough variability for denominations
  • 1
    $\begingroup$ Your main problem as I see it will be in preventing counterfeiting. Either your currency needs intrinsic value (is it very rare and reasonably useful or perhaps I can eat it for dinner), or there must be one controlled source. A Jack or other oddly shaped object would do, but if you can make them to easily, there will be problems. $\endgroup$
    – user29032
    Apr 19, 2017 at 3:16
  • 1
    $\begingroup$ With limited metalworking, chemistry, and medicine, what is it that makes them a tier 6 civilization rather than tier 7? $\endgroup$
    – Ben S.
    Apr 19, 2017 at 6:35
  • $\begingroup$ @BenS. Technology has improved to a point where large-scale farming and fishing industries are able to provide food for the general populace. Individuals can have occupations other than "obtain food" or "take care of children": there are full-time musicians, priests, politicians, etc. There is rich culture. In my mind, this is sufficient to be called tier 6. $\endgroup$
    – Makst
    Apr 20, 2017 at 2:32

3 Answers 3


Salesman #1: You're crazy with the heat. Credit is no good for a notion salesman.

Salesman #2: Why not? What's the matter with credit?

Salesman #1: It's old fashioned. Charlie, you're an anvil salesman -- your firm give credit?

Charlie: No, sir!

Salesman #1: Nor anybody else!

The Music Man, "Rock Island"

Writing is believed to have been invented originally for goods logging and tracking for commerce. I believe your best bet would be for your society to have bypassed directly over "hard currency" to credit.

The problem with hard currency is the need for it to be intrinsically valuable. A bauble of silver for a cubic meter of seaweed, or whatever. The problem, as you state, is the unlikelihood of metal working to be feasible underwater.

This is a different dimension of a problem experienced by the Venicians in the Middle Ages; responsible for handling thousands of "pounds of silver and gold" worth of trade, they needed a method to keep track of goods without actually counting out hard money over and over again.

They invented the cheque. (Muslim traders used a form of cheque as well, and JewishHistory.org claims Jewish traders invented the cheque. The Dutch Republic in the 1500s had professional "cashiers" who handled cash for citizens, charging a fee; they provided additional services, including cash-on-demand to anyone bearing a written order. But I'm going to credit Venice today.)

Cheques, promissory notes, bills of exchange; these negotiable financial instruments were all about notating a large value worth of goods onto some recording medium, and then using that recorded value in place of the goods themselves. The bearer of the instrument could then extract the value on demand.

This was the bases of money in the world from the middle ages 'till Nixon killed the Bretton Woods system, and Federal Reserve Notes could no longer be converted to hard currency. Yes, pre-Nixon you were still spending gold and silver, you were just using paper certificates to do so.

Your underwater civilization just avoided the hard currency middle-man. From the beginning, they either did hard-barter with goods, or traded negotiable financial instruments.

Perhaps they started using shiny rocks, or pearls, or volcanic rock pulled up by "miners" who could swim down to the lowest depths of their ocean, but for underwater critters these goods would be even less convenient than they would have been for us.

So from the beginning, they would have come up with a system of trade involving negotiable instruments, payable to the bearer on demand. A group of critters farming fruit would trade an invoice for fruit in exchange for some good they needed; that instrument would be further traded until somebody needed some fruit, at which point they'd bring the instrument to the fruit farmers to demand their goods.

Now, negotiable instruments are much easier to counterfeit, in theory, than hard currency, which is one of the many reasons why hard currency remained popular until even today. So your critters would need some way to validate these negotiable instruments.

  • Do they have a form of writing? This would essentially emulate the early banking systems on our world; an instrument would be written by the possessor of a good, and countersigned by trustworthy individuals to prove the value of the note, which could then be traded freely.
  • Even without writing, verification is possible. The "split tally" system was very common in the middle ages amongst predominantly illiterate society. A stick would be scored with a system of notches showing taxes owed and then split lengthwise; each side of the deal would receive one piece of the stick. You could then validate the document by putting the sticks together; while you could modify your stick, you couldn't modify the other stick without possessing both, proving that some change had been made.

Here's a really, really crazy idea: Underwater blockchain. Bitcoin works by keeping a long, immutable ledger, distributed around the world known as the blockchain. The mathematics involved allow you to prove the correctness of a ledger. New transactions are added to the blockchain in such a way that they become a permanent records. What if your critters used something similar to record transactions? ...and what if the blockchain was actually whalesong? Let's assume that whales on your planet are not sentient... or at least one species known for it's song isn't. A group of your critters learn how to interpret the whalesong, and how to encourage these whales to modify the song. Let's handwave that the whales have "photographic" accoustical memory, that they refuse to change songs they have learned, but learn new songs easily. You now have an underwater banking system whereby transactions are recorded by "tellers" who literally "tell" the transaction to a local whale, who then weaves that transaction into the songchain it sings. Other whales hear the new song and share it. Anyone who wants to retrieve a transaction "hums a few bars" to the nearest whale, who then gladly sings the rest of the song. Because songs can only be appended to, never modified (the handwave), by listening to the song you can verify that the bearer of a financial instrument actually bears the legitimate instrument, and can then provide them with the good (logging it into the songchain, of course).

We can further stipluate that whalesong is generally at the lower range (or upper range) of the frequencies our critters can hear; in general, it's just the normal background noise of the ocean. But a specially trained critter can listen to the chainsong and interpret it, and encourage local whales to append to the chainsong. The whales just do what they have always done: share songs with each other. Their song carries for thousands of miles in the ocean, ensuring that every transaction is eventually recorded everywhere in the world, allowing you to "spend" your instruments anywhere where the song has been recorded.

Now, I'm sure somebody with a background in information theory could prove that the type of whalesong which travels such long distances conveys too little information to be able to log EVERY transaction on an entire planet, but if we're willing to suspend disbelief a little bit, the songchain would only be used for large, interocean transactions. Local networks of trust would be good enough for day to day operations, with enough signatures on an instrument or a tally-shell business works fine. Long distance trade could be handled by songchain however.

  • $\begingroup$ Very interesting! Writing would most likely be the cuneiform mentioned in this answer, which could support signatures through the use of seals, so negotiable instruments could certainly work in the absence of any reasonable hard currency. The whalesong blockchain is fascinating, but I think such whales would end up being so significant to the design of the world and culture of my creatures as to possibly overshadow them. $\endgroup$
    – Makst
    Apr 20, 2017 at 5:29
  • $\begingroup$ I can see that concern, @Makst, the songchain was mostly a cool idea I thought up while I was typing and I had to share! However, I would point out that these singing whales, IMHO, would be as important, but as background, to the economy as, say, horses in a western. Obliquitous, but in the background sort of way. $\endgroup$
    – Zoey Green
    Apr 20, 2017 at 18:11
  • $\begingroup$ The biggest problem with the songchain that I see, @Makst, is having to explain it. Depending on the size of your story, it may be good enough to just mention it, or it might be worth explaining (Moby Dick style)... and it's the second form that I really see danger of overshadowing the real story you want to tell. It all depends on the amount of handwave you are willing to live with. $\endgroup$
    – Zoey Green
    Apr 20, 2017 at 18:13
  • $\begingroup$ Finally, @Makst, the nice thing about negotiable instruments is that they work well alongside hard currency. There's good hard currency suggestions on this question, but they all suffer from bulk; and depending on the build of your characters they may or may not find carrying large amounts of minerals or whatever handy. I think it may be an interesting story dynamic to see the lower classes lugging around minerals while the middle and upper classes use financial instruments... very modern USA. $\endgroup$
    – Zoey Green
    Apr 20, 2017 at 18:14

I suspect that I don't know nearly as much about microeconomics as the other respondents, so there could be some significant problems with my suggestions, but I thought I'd give it a shot.


They're reasonably small, fairly durable, and since they're produced by oysters they don't require advanced technology to obtain. They're also somewhat rare because they take time to produce and are difficult to imitate convincingly. The difficult part would be creating different denominations - perhaps they could distinguish them by size, or introduce some factor during the cultivation process that would give them a distinct smell or texture (perhaps by using different species of mollusks or by feeding them differently).

Hard Spice

I'm envisioning something along the lines of rock salt, but much more resistant to erosion by water - something with a distinctive taste that generally wouldn't break. Different denominations would be represented by different spices, each with their own taste. It probably shouldn't be something that they'd actually want to eat, just something that was distinctive and non-toxic - you don't want the whole market to crash because someone discovered a popular new recipe that uses cumin.

  • $\begingroup$ "Your great grandfather almost didn't survive the Great Black Pepper crash of '07." I like the idea of using a spice or mineral as hard currency, based on the alien's sense of taste. $\endgroup$
    – Zoey Green
    Apr 20, 2017 at 4:49


Is the most valuable currency. No matter the proposed value of an object, if you do not trust that you can change bank notes / coins / gold / platinum / diamonds / etc for something else, you will not trade.

One of the useful parts of currency is that you don't need to keep translating two chickens into 50 kilo's of apples. And 10 thousand apples make one cow. Etc.

So if your creatures have very good memories, what they probably need without active sensory input, as hearing and smell are passive, you need to remember where (your) stuff is.

If that is to much for you, use shells from certain snails for currency. Just got to make sure they are hard to forge.

To clear it up a bit. Every one has a running tab when you buy from one another. Or better yet, a very broad system of non-enumerated credits and debts.

So let's say I like to drink a beer and I go to the pub a few times a week to do so. The bartender knows me, and I have no easy way of buying each and every beer, so I have a tab running. Either he remembers, or notes it down. Now, sometimes the bartender will need to close the tab with me. Let's say he does so every month. 4 weeks * 5 evenings * 3 beers = 60 beers. Let's say that is worth 2 chickens. Or he clears the check ones every year. That might be worth a sheep. But if that sheep is worth 13 months of beer, I just have pay for a new month already.

Recommended reading: Debt: The First 5000 Years.

  • $\begingroup$ I don't really understand how trust can be used as currency. The value of an object fluctuates based on many factors, including the individual looking to purchase it. How can someone use trust to purchase something? Could you clarify? $\endgroup$
    – Makst
    Apr 20, 2017 at 2:47
  • $\begingroup$ Lets say you create a statue of 1000kg of gold. But if no one wants it, it is still worthless. Now you say, you can do a lot of things with 1000kg of gold. Yes, sure. But if you are starving no amount of gold will help you unless you can trade it for food. The worth of an object is a very subjective thing. It's just very convenient to all agree on the worth of certain items. $\endgroup$ Apr 20, 2017 at 7:47
  • $\begingroup$ Hmm, I don't think this system will work for any economy larger than a small village. On a larger scale, it's impossible for every person to personally know and have an agreement with every other person. Globally deciding in advance what everything is worth and never changing it is pretty much the opposite of how a real market works. $\endgroup$
    – Makst
    Apr 20, 2017 at 14:34
  • $\begingroup$ Didn't say it was perfect. And it does not scale well, for us humans. Inflation is quite a modern thing, prices were stable for a long time. For about 100+ years Roman soldiers were paid the same amount. Maybe it gives you an idea about what else is possible without resorting to things we are very familiar with. $\endgroup$ Apr 20, 2017 at 14:46

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