I don't know how many words there are for various types of human emotions in the English language. In our everyday vocabularly, there is probably about a hundred, from something crude like hungry all the way to more abstract concepts such as pensive or dreamy. Maybe English doesn't have enough words, but for most practical porposes, it looks like we have more then enough to go about our daily life.
But these emotions still give only approximations of what they are actually like. Part of this is just because language can never capture an actual experience. For example, you may have used the expression knock kneed, but that doesn't quite describe what it feels like to actually be so afraid your knees are knocking together.
But even dealing with such mundane human emotions as hunger, it is hard to describe what is actually going on, because the emotion exists as a ratio between two things. That is, it is a relationship between the person who wants the food, and the food itself. The subjective experience of hunger is a third part of the equation. So to say you are hungry is misleading, since there are really three related phenonmenua going on.
Now, hunger is a simple emotion. Emotions like love are not. Often we will say something like "I want someone", we actually mean something like "I want this person to want me to want them", not to mention something like "shopping for dishwashing soap with this person makes me giggle". Where is the emotion there? In the wanting, in the feeling of self-worth that comes from being wanted? Or to see someone be happy because of you? Is it in the giggles, or in the dishwashing soap?
On a normal level, we don't need to know the precise value of these things, just like for normal purposes
.2679491924 makes a perfectly adequate tangent of 15 degrees. However, the actual tangent of 15 degrees can actually be described by a number of formulas that involve taking ratios of numbers that are already radicals. The true tangent of 15 degrees is (1-cos30)/sin30.
By itself, this isn't that much of a problem, but when you pass this from equation to equation, and do hundreds of these problems, the inaccuracies begin to pile up, and soon the answer is totally wrong.
Philosophical researchers should be just as careful that they keep the entire emotion in mind, and not just the common everyday decimal approximation of the emotion. If a philosopher wants to know what "love" is, he should pass all the aspects of what it means to feel love, and be loved, and be a lover, through the equation, and only then will we be able to accuratly describe what human emotions are.