1. Your soulmate will know you instinctively
The essence of a soulmate is someone who has a deep connection with you. Someone who knows what you are thinking without having to ask. Conversation is not always necessary as they will know how you are feeling. This might be because they have been where you are right now, or simply because they know you so well emotionally.
On the other hand life partners have a relationship based on intellect. Attraction is physical but is also driven by a desire to learn more about each other, as opposed to the emotional rollercoaster experienced by soulmates.