@Radiant Heart: NOTE: This long post is personal opinion and while I believe it to contain truth I do not pretend that 1) this truth is a complete and total thought 2) that this thought is correct in all aspects. I reserve the right to change my mind when new knowledge provides the need to remove old knowledge.
"Knowledge is Power" and "Power corrupts."
My basic thought? They work together and the 'power' of 'knowledge' 'corrupts'.
I'll define first what I think of the three terms. Then the meaning behind the sayings. Then how I might amend to better express 'truth'.
POWER: This is to be understood as the capacity for a human to shape his/her world with greater ability than others who would be said to be 'less' powerful. A rich man has more currency with which to acquire more material goods. A charismatic speaker has the ability to sway multitudes. A genius has the ability to develop more in his field. Spiritual power (or power of Will for my secular friends) gives a person the ability to eschew typical human boundaries.
I would assert that not all power is equal. To be very brief about this as I could go on endlessly. I believe that powers that rely on compensating for fear (the fear of being power'less' or the fear of being incapable of the ability to shape his/her world to any degree) are the weakest (all disciplines concerning the material world) - while powers that focus on abating the fear of power'lessness' are stronger (of which I believe there are only two, with a myriad of choices within. Spirituality(Will) and Philosophy).
KNOWLEDGE: The capacity to have gathered data whether it be in the form of facts or skills or experiences. I burned myself - I should not touch fire. Knowledge is a form of mathematics. Combine the previous statement about fire with: These gloves are fire proof. I burned myself = I should not touch fire. I burned myself + these gloves are fire proof = I should not touch fire without these fire proof gloves.
I believe knowledge without 'wisdom' as I defined it for myself earlier is an inability for people to do this form of mathematics. Ultimately this why humans attach themselves to only a handful of concepts and push those concepts as 'truth'. Religion is not the only such set of 'facts' to embrace this. Science, nationalism, family, and a vast list of many other 'truth' concepts are due to the inability or unwillingness to add more to the current 'knowledge' equation any human has.
This is regardless of whether that person expresses the desire for more and more knowledge. I have seen many people who claim to want more knowledge, but live their lives by several personal truths as if those truths were realities for the rest of the population. This is what philosophers refer to when they discuss a persons private universe.
CORRUPTION: Is simply change, though it is undeniable that it has an almost universal negative connotation. So let us say that it is negative change. Cancer is a negative change of cells within the body that are anathema to life systems. But that is 'simple' corruption. Greed is the corruption of need. How can one come to a conclusion without boorishly debating "moral relativity"? I believe the answer lies in the mathematics of knowledge (without professing to have developed the correct calculations myself)
Need is basic life functions required to sustain mental and physical health. An animal knows what it needs. A human does not (hence, why the concept that animals are inferior to humans is questionable). We know that water and food are 'needs' and then confound it with corrupting items like 'soda' or 'fast food'. I am not exempt from this.
Greed is an excessive function. It is driven by fear (the fear of 'have not'). It is also the absence of satisfaction with 'need'. It has nothing to do with 'Evil' in a metaphysical sense (at least for the purpose of this exercise). It has to do with the corruption of precise and lucid thought (practiced by animals, but no longer by man). It is a confusion of 'need' into the illusion that what we 'want' is also what we 'need'.
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So - "Knowledge is power". As we see (if my definitions are to be believed) - knowledge is power. Knowledge provides aptitude through fact, skill or experience. Aptitude provides one to effect greater change - which is, at least for this exercise, power.
Corruption is a negative change in something.
The missing component is wisdom - or the ability to do the mathematics of knowledge which I call "wisdom".
"Power Corrupts" - Power, as we see provided by knowledge, does not come with wisdom. Knowledge - Wisdom = Corrupt Power. The deficiency which corrupts power is a human one not inherent in "power" itself.
So: "Knowledge, with or without the ability to do mathematical knowledge (wisdom), is the ability to effect change (power)." Knowledge is Power
And: "Knowledge, without the ability to do mathematical knowledge (wisdom), is the ability to effect change only within a personal universe (power + illusion)." Power Corrupts is correct, but is inefficient as it doesn't explain "Why" power corrupts. People who cannot put together pieces will not understand "why" and therefore think, incorrectly, that it does not.
Effecting change only within the spectrum of one's personal universe is, ultimately, corrupting to the shared gestalt Truth of humanity (the argument that such a truth does not exist is not part of this exercise). I will assert only that such a Truth does exist. Though I will not assert whether it is a collective agreement between humans or divinely inspired.
Need with Power (Knowledge) without Wisdom (or the ability to ascertain my proposed 'gestalt Truth' through mathematical knowledge) is Corrupt Power.
The assertion of "Power Corrupts" is = All human knowledge lacks the ability to ascertain 'gestalt Truth'.
Without wisdom - you cannot have power that is uncorrupted, And now we are at the very purpose of philosophy and spirituality (whether they are successful or not). They are the attempt to form a gestalt Truth that is bereft of the corruption of the personal universe that lacks wisdom and is the source of the statement "Power Corrupts".
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THE WELL:
Morrigan's greed is due to her fear of the lack of control. She wants knowledge, but lacks wisdom. This is very clear between DA:O and DA:I. She has gained some wisdom - evidently through the birth of Kieran. Her personal universe has expanded to encompass more than just herself and therefore is one tiny step closer wisdom. But it is clearly not enough to abate her fear of control. She's willing to pay the price of the Well regardless of how that price will impact Kieran (if she has a child) she is obviously still no better than she was. Eternally selfish and locked in the illusion of her personal universe.
Her desire for the well clouds her judgement. The Well takes on an almost Oedipal context. Her fear of being without control leads her to being without control. (the same holds true for the Inquisitor).
Knowledge is Power: Morrigan gains the power of the ancient elves through their knowledge. It corrupts her judgement through greed. It is likely she knows that "not all costs are worth paying" yet she chances it. In this instance - it turns out her fear of being without control is self-fulfilling. I believe we even see a negative implication if Inquisitor drinks from the Well. The Inquisitor is forced to attack Morrigan (even if only to subdue her) and therefore has lost agency through the craven pursuit of knowledge without wisdom.
Without the control of Mythal - the power still remains corrupting as it has no context. Morrigan will use this power as SHE sees fit. Who is Morrigan to use power in such a way?
It is fascinating to me that many people I have met will say: "If God exists he is evil because he does not cater to my whims." but then will say "I want knowledge so the world must cater to my whims." It is a hypocritical double standard possessed by many self-righteous 'clever' people who worship knowledge and why I find Saint Augustine's scathing opinion of 'clever people' to be in conjunction with my own.
TL;DR - Both "Knowledge is Power" and "Power Corrupts" are true. All knowledge is corrupting.