I think these 3 are a given:

Semantics - imprecise language or words that mean one thing for one person and something different to the other.

Perception of the relevant facts - different exposure to news and related anecdotes/experience, etc.

Relative weighing of the principles - one person might think the countervailing interests balance out or favor one side, while another person might think they favor the other.

What are some others?

Because we are all individuals with our own opinions.

Different personalities and different opinions/views, there will always be someone who disagrees with someone else.

Imagine a debate in philosophy between two people Lets say Dennett and Chalmers.

What is standing in the way of their agreeing?

well to go through the psychological list

1) they are 'supposed to' disagree

but that isn't very useful so we will skip over that

2) because they want different things

maybe for some reason Chalmers is more comfortable with qualia existing and Dennett is not - one strategy if debate would be to expose that and call it a bias

3) because they have a different set of assumptions

any belief that you might have is built on a series of assumptions - in thecase of dennet and chalmers a huge network of assumptions that describe different worlds in sense. But neither side initially knows exactly what those assumptions are. So I might wonder "if I disprove X (where X is a fact that seems to support your conclusion) will your world view come tumbling down or will you just say - I don't really care then y must be true"

So what strategies does each side have open to them? well they will probably run through each of the other person's assumptions and tackle them.

these assumptions will hide in the definitions of words and implicitly ignoring other words

Because some people get the wrong information from places that they do not know what there talking about. please vote !!!!!!!

http://www.createdebate.com/debate/show/ should itbelegaltohavesexwithdogs_3