Spiritualists championed a derivative of union theory that asserts that the union, rather than metaphorical, is the literal fusion of two souls (or two half souls) to form one new soul.
Aristophanes recounts how when God first created humans, we were round, spherical, androgynous forms. We had no gender but instead had four arms, four legs and two faces. However, God decided to punish us for our arrogance. He severed humans into two, leaving each human with two legs, two arms and one head. In doing so, he condemned us to a lifetime quest of finding our other half and unifying to become whole. This quest to find the other half of our union is what we now call love. In searching for love, we are not just searching for another person with which we have a deep emotional connection. We are searching for a part of ourselves, our “other half”. When we fall in love, we find a soul which completes us, helping us to further understand ourselves in the process. When we fall in love and build a union, we become a shared identity and form a new soul. Both individuals play a central role in forming that soul and new identity.
The whole argument hinges on the idea that humans have souls in the first place. No adequate theory pertaining to the existence of human souls has overcome the challenge of how a non-physical soul can interact with a physical body. Why, for example, when my "soul" wants to move my arm, does my arm move, and not your arm, or the cat's arm? The laws of physics do not permit the interaction between a physical object and a non-physical one. Without proving the existence of the soul, spiritualists cannot prove the theory of love as two souls coming together. Even if we can accept the existence of a soul, this view of love is constructed around monogamous, binary views of love and sex. It does not extend the existence of love to those in polyamorous relationships. This restrictive and binary view of love is outdated in the modern world where polyamory is increasing and a more progressive attitude towards love is emerging.
[P1] Humans have souls. [P2] When we fall in love, the lovers' two individual souls merge to form a new complete soul.
Rejecting the premises
[Rejecting P1] Souls are not real.