In the final phase of his career, Solomon returned with renewed intensity to the philosophy of emotion, integrating decades of reflection into a comprehensive vision of the passionate life. Building Trust (2001, with Fernando Flores) extended his interest in business and applied philosophy by exploring trust as a foundation for cooperation, communication, and social order. With Spirituality for the Skeptic (2002), he sought to articulate a secular, human-centered account of spirituality rooted not in dogma but in meaning, responsibility, and emotional engagement with life.

This period was marked by a series of major works on emotion, collected under the theme of “The Passionate Life.” Not Passion’s Slave (2003) challenged the idea that emotions are merely forces that overwhelm reason, instead defending their role in choice, agency, and meaning. In Defense of Sentimentality (2004) further rehabilitated feelings often dismissed as superficial, arguing that sentimentality can reveal moral depth. His culminating work, True to Our Feelings (2006), offered a comprehensive theory of emotions as central to moral life, blending existentialist insights with contemporary philosophy of mind.

Solomon also continued his long engagement with existentialism and its figures. Living with Nietzsche (2003) presented Nietzsche as a guide for living with integrity, courage, and joy, while Dark Feelings, Grim Thoughts (2006) revisited Camus and Sartre to examine how philosophical reflection emerges from experiences of despair, absurdity, and struggle.

Phase IV thus represents the culmination of Solomon’s philosophical trajectory: a mature synthesis of existentialism, ethics, and the philosophy of emotion. In these works, he underscored the way emotions shape trust, spirituality, self-understanding, and our moral orientation toward the world, leaving a legacy of philosophy as deeply lived and profoundly felt.