What does Sartre mean by “Existence precedes essence?” What is essence and existence? What makes him conclude this? What further effect does this have on meaning, value, and freedom?

Essence in this case refers to the ancient philosophical idea (most closely associated with Plato) that all things have a predefined, ideal set of characteristics. For instance, the Essence of a chair is that it has four legs, a back, and people sit on it.

However, not everything matches its Essence. You might have a chair with three legs, or a broken back, or that no one sits on. The actual details of a particular chair make up its Existence.

The idea that Existence precedes Essence is that –for human beings –there is no predefined pattern that we must fit into. We live our lives, and that in turn defines what we truly are, not any idealized set of characteristics. This idea is the heart of Sartre’s version of Existentialism.

The implications are that we must create our own meaning, place our own value on our acts, and that our individual freedom is absolute and unbounded.

As a side note, Sartre, although an atheist, gave what I consider to be one of the best ever descriptions of God, as the “Union of Existence and Essence”, meaning that God is the full Existential realization of every perfect, ideal or Essential attribute of God. Sartre, of course, described that as an impossibility, but it is also a good description of what a believer believes God to be.

Does Existentialism, in general, synthesize well with other philosophies such as Phenomenology?

The term phenomenology means the study of phenomena, where phenomena means observable experience. The chief difference between phenomenology and empiricism (which also studies observable experience) is that phenomenology tends to focus on subjective, first-person experiences of the world, whereas empiricism aspires to create an objective, third-person experience of the world.

The “existence” in Existentialism, on the other hand, comes from the idea that “existence precedes essence,” where an object’s essence is viewed as a set of indispensable defining characteristics common to all such objects. A chair, essentially speaking, is a four-legged object that people sit upon; a mirror is essentially an object that casts a reflection. The existentialist claim is that human beings have no such essence. We, as human beings, create our own self-definitions through freely willed actions. We cannot be predefined, our essences are not predetermined, but created in each new moment through the acts that compose our existence.

What the two movements have in common is a radical emphasis on the first-person perspective, which helped the Phenomenology of thinkers such as Heidegger and Husserl to become a major influence on the familiar French Existentialism of Sartre and Camus. Rather than saying that the two philosophies synthesize well with each other, therefore, it might be more accurate to say that the most familiar form of existentialism is itself a synthesis of the first-person perspective of phenomenology with the will-driven radical freedom of thinkers such as Kierkegaard and Nietzsche.