What is a sankalpa?

A saṅkalpa is often defined as simply “a desire.” In Yoga circles it takes on a more affirmative meaning as “intention” or “resolution.” And yet, teachers of Vedanta use it with more nuance. To be exact, a sankalpa is the force or impetus that takes a thought (“Red, shiny, juicy apple”), applies a value or worth to it (“The apple looks delicious”) and turns it into a desire (“I want that apple”). A sankalpa can have a beneficial or negative effect. For example, one might establish a sankalpa that leads to cultivating a more dharmic life, or one might have another kind of sankalpa that projects false attributes onto an object, creates attachment and leads to suffering.
The wise remind us that it isn’t the senses that create our problems, but the mind and its ability to superimpose fanciful imaginings onto something. When a thought arises in the mind about a particular object, we can either be indifferent or pin a certain value or worth to it. In turn, applying value to an object evokes emotion which inevitably leads to a sense of want.
If the desire is strong enough, we might begin to think about the object repeatedly until we develop a strong affinity for it. It’s this condition, from thinking “May I have that” to “I need that,” that binds and causes suffering. If our desire is thwarted, it leads to anger, which in turn leads to the inability to tell the difference between what’s true and what’s not. The Bhagavad Gita tells us “The mind that follows the wandering senses loses its capacity to discriminate, just as an unmanned ship is carried away by the winds of its own destruction.” (2.67). Thus, what starts as a small seed has the potential to grow into a state of extreme mental agitation that’s hard or close to impossible to escape from ("I must have that apple!").
Vedanta advises us to catch an attractive thought early before the mind has a chance to construct a story or attach any false value to it. For example, it’s typical for people to fall in love with an attractive person, even from a distance. Standing in a cafe waiting for the barista to make our coffee, we might eye a good-looking person just feet away. Next, the mind begins to create a whole story regarding their “perfect physique” and “indelible charm” (projections) and the possibility that we’ve finally found our one and only soul-mate. We might believe they are the single thing missing in our life and imagine ourselves dating, moving in, marrying, and spending the rest of our life together in perfect contentment. All this without having even met them! What started out as a simple thought (“attractive person”), rapidly snowballed into a whole romantic life story about living happily ever after. When our soul-mate finally picks up their coffee, thanks the barista and leaves, we feel a little heartbroken having not even made eye contact with our newly-made object of desire.
One way to check a sankalpa is by analyzing the object and verifying that it isn’t just the mind constructing another story. We need to always put all our strong desires under a microscope. When the seed of a desire (sankalpa) arises as a thought, instead of applying fanciful imaginings to it, we can investigate it to see if it reflects the actual truth/reality. Or we can choose to simply ignore it and let it die of its own volition. Like holding a hot potato, any initial discomfort from a sankalpa will dissipate on its own if we just allow it to. Sankalpas only develop into binding desires with our involvement. In the end, all sankalpas are just thoughts. It’s up to us to manage them in a way that avoids any suffering.