Email Question: - Logical Thinking and Spirits

I received an email from a gentleman asking about how to determine whether his parents are at peace. His background is similar to mine, a background in science- so we were "taught" to both be logical thinkers. Because our logical mind always tries to explain things and usually discards unexplainable events, and calls things "coincidences" we don't recognize signs from spirits (those who have passed into the light). For the person that doesn't have mediumistic abilities, the only way that those spirits of passed loved ones can communicate is by coming to us in our dreams.
In fact, in this case, both parents did appear in this man's dreams. One thing I've noticed in speaking with a number of people, however, is that usually within the first year or two loved ones who have died will appear in a relative's dreams. However, that tends to fade.
After thinking about it, I believe that the spirits have given the person left behind, a year or two's worth of signs that they're okay in the afterlife. After that, they hope the living relative moves on with their lives and stops grieving. It's important that we who are left behind understand these signs, and that our loved ones who pass want us to move on.
We can, however call to those who have passed, and they will hear us. More on this in a future post.