A reasonable return on capital is an underpinning cornerstone of nearly all economic activity that is based upon an agreed medium of exchange rather than barter.
However, the 'interest' that most of us mean when we speak of the subject is fiscal/banking related and was, curiously enough, 're-invented' or, better, 're-implemented' by the emergent banks of the industrial revolution from a concept long held in contempt. An aside is that this principle is one of the main reasons why Anti-Semitism was rife long before the Nazi's ever came along, for the displaced and thus landless Jewish businessmen made use of it to expand their wealth at the expense of the powerful ruling families of Europe.
Anyhow, the subject of modern banking interest charges is a whole different ball game and is probably the biggest 'con' the world has ever seen.
I'm sure that most people are aware of it but I'll reiterate it for clarity. The modern banking system runs on what is called, disarmingly, the Fractional Reserve Principle.
What this means, in simple terms, is that if you deposit $100 with a bank then it enters that into the books as a deficit i.e. it owes you that money. However, it also treats it as an asset when it comes to making loans. A bank is allowed to lend out 90% of the capital it has deposited. So it can lend $90 of the $100 you gave them. Some of this money it will 'invest' in various schemes upon which it will hope to make a sizeable return. Also, some of this money it will 'lend' to private individuals with a repayment value, dependant on the term, that can be as much as double or triple the original loan.
That strange 'leverage' is down to the arcane machinations of the mathematics of compound interest. I won't go into that here as even as a qualified economist and accountant (AAT certified) I still don't understand how it was ever allowed in the first place

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The short explaination is that most of the repayments you make in the early terms of a loan merely go to pay off the interest with a small fraction reducing the principle. That's how, for example, in the first year of my first mortgage, I paid several thousand pounds and yet only reduced the amount I owed by £150 :faints:.
Compound interest, if you'll forgive the pun, only works, as
Ceicei says in the interest of the banking corporations. It ties a millstone of debt around almost everyones neck that serves only to feed the banking system and is economically unproductive.
It's a sibling of other economic 'sinks' such as currency speculation and the stock markets in that it is non-productive money and actually reduces the productivity of genuine capital. What I mean by this is that all it does it siphon money into the banking system and does not act as an economic multiplier for general wealth, which is what a tangible business that manufactures 'stuff' actually does (which is why trade got going in the first place and is the blood upon which the parasite which is banking feeds).
Anyhow, enough economic blathering

. Not all economists feel this way and I'm wondering, now I know we have similar backgrounds, if
Tellner has a different take on this than me?
Sub-rosa-
I'm a Keynsian at heart by the way,
T and have a mighty disdain for the 'childs' economics that is monetarism.