It seems that many cultures have some concept relating to a person's purpose or destiny in life, and in American paganism and its many sub-branches these culture specific terms tend to get used interchangeably, often equated to the term "fate". Fate, of course, is the idea of a predestined or predetermined outcome in life which cannot be altered or affected by human action. Many Greek tragedies, such as Oedipus, are based on this idea which is personified in Greek mythology by the Moreia (the Fates) who create the "thread" of a person's fate, measure it, and cut it at death. Loving semantics as much as I do, I feel the need to point out that the terms equated to fate are not actually equivalent to each other and in fact often have very specific nuanced meanings. I thought it might be good to write about some of the most commonly used words and how I personally understand them, although I have to be clear that this is purely my own viewpoint; I am no expert. However I think even an amateur attempt at explaining the different terms could be helpful and also could provoke some great thought and discussion. I do want to stress though that this is my own understanding of the concepts, based on my research and study.
First let's look at the most common term: karma. At this point there are two very different ways to understand karma, which may be labeled the Eastern and Western views. The term itself is from Saskrit and means "action" and is a concept found in both Hinduism and Buddhism; this is what I refer to as Eastern karma. Effectively karma is a neutral principle, the result of the sum total of our actions in this life and previous incarnations. Karma is what directs the circumstances under which we will next reincarnate. We can affect our own karma by choosing the actions we take, because all action inherently creates karma, but karma works on a cosmic scale. I like to think of (Eastern) karma as something like painting; each and every color choice and brush stroke, i.e. action, effects the end result. In contrast Western karma takes a more immediate approach, espousing the idea that karma works on a small, fast scale with the effects of our actions appearing not only within our lifetime, but also sometimes in the same day as the action. The Western view also sees karma as a moral principle, with "good" and "bad" karma based on actions. At its simplest this can be illustrated by saying if you do good, good will happen to you and if you do bad, bad will happen to you, rather like a spiritual ATM - put money in get money out, overdraw your account get charged fees. The most common view of this principle works entirely on the idea of an inherent good and bad value system to all actions, and is supported by the idea that either karma itself is a semi-sentient force or that the Gods enforce it. A less common view related this idea to energy manifestation, as a way to explain why the energy we put out returns to us. When discussing karma or when someone refers to karma it is important to know which view - Eastern or Western - they are applying because the two are very different.
Next we have the concept of wyrd. Wyrd is an Anglo-Saxon word, corresponding to the Norse urd, and means, roughly, "to come to pass" or "becoming"; related to this is the concept of orlag, meaning "from the law". As it was explained to me, orlag is the sum total of our past actions as well as those of our ancestors - we are born with a fixed orlag based on what has come to pass before our birth. Orlag effects all creation, including the Gods and spirits, as well as people. To quote Bauschatz: "This past includes the actions of all beings who exist within the enclosing branches of Yggdrasil: men, gods, giants, elves, etc..... it is such actions that form the layers or strata that are daily laid in the well by the speaking of the orlag. The coming into the well is orderly and ordered; events are clearly related to each other, and there is pattern and structure in their storage.” (Bauschatz, 1982). Orlag effects us because it is the base form which we move forward, but wyrd is the active principle created by us during our lives, which in turn creates orlag. Every action we take is based on our wyrd and orlag and further creates the wyrd we are then living with. Wyrd and orlag are both flexible and fixed; like water flowing in a river and the bed of the river itself. The river bed shapes where the river flows and directs the water but the water can change the shape of the river bed. So it is with wyrd - we shape our wyrd by our choices but our wyrd creates orlag which in turn directs our lives. Some people argue that orlg and wyrd are the same concept, and that may be so, I just find that it is easier to grasp them as separate but interlinked concepts. The analogy of weaving is often used to describe wyrd, and I tend to see wyrd as the weft and orlag as the warp. Freewill is an important aspect of wyrd, as we always have choices on how to act within the circumstances we find ourselves in.
Dán is an Irish word that translates as "fate" - and also as gift, offering, craft, calling, and poem (O Donaill, 1977). It is a complex term but is often understood as the fate or destiny that a person is born with. There is a saying that goes "A man won't drown whose dán is to hang" that illustrates this idea that dán is inexorable and inescapable. This term out of all of the ones we are looking at most closely resembles the Greek idea of fate, although the Irish appear to have lacked the personification aspect of fate seen in the Greek.
Even if we just look at the roots of each word we can see that there are differences in there meanings. Karma comes from the I-E root of kwer which means to do; wyrd comes from the root wert which means to turn or rotate; fate is from the root bha which means voice (I couldn't track down the I-E root of dán). Each root meaning connects logically to the modern meaning I think, and shows the subtle differences between the terms.
While I can see why it is easier to use the simple equivalents when discussing the different terms I believe that it is better to understand the nuanced meanings of each term. Each one has its own layers and depth which reflect the culture and world view from which they came, and for modern pagans more can be gained by using them properly than by reducing them all to a Greek concept of fate. There is also a wealth of understanding to be gained by studying each term, in depth, individually, which I encourage people to do if the subject interests them.
Bauschatz, P., (1982) The Well and the Tree: World and Time in Early Germanic Culture
O Donaill, N., (1977) Focloir Gaeilge-Bearla