The idea that human reasoning is largely (but not exclusively) based on Metaphor Systems. Originated by Michael J. Reddy 
essay on the Conduit Metaphor, taken up with vigor by Lakoff and Johnson.
Explained in a podcast episode, How Do Metaphors Work?
An example of such a system is Love Is a Journey. It's easy to list individual metaphors that are examples of this system:
* Look how far we’ve come since that first date. * Our marriage is at a crossroads. * This relationship isn’t going anywhere. * We may have to go our separate ways.
In the jargon, Love is the Target Domain and Journey is the Source Domain.
Two domains, T for target, S for Source
You can think of both domains as being concerned with similar things:
Ideas and relationships and attributes, oh my!
In a love affair, you'll face choices, just as you're likely to face in a journey. You also have goals – some sort of destination – in both cases. In the case of a love affair, the goal might be to have someone to care when you're on your deathbed. For a journey, it might be see the Longaberger Big Basket Building in east Newark, Ohio, USA.
**The claim of conceptual metaphor is that often understanding and problem solving are done *in the source domain* and then translated into the target domain.**
Mapping between source and target domains (source on the right)
Note that not everything in the source domain has a corresponding thing in the target domain, and vice versa.
Let's explore that.
I think understanding what someone means is the easier case. Understanding the Crossroads Metaphor.
More interesting is using knowledge of the source domain to solve problems in the target domain. Problem-Solving in the Crossroads Metaphor
Especially when it comes to problem-solving, there are two snags:
1. The Extra Source Element.
2. The Missing Source Element.
----- See also: Conceptual Metaphor as Metaphor, Propositional Metaphor, Comparison: Conceptual and Propositional Metaphor, Abstract Source Domains, Comparison to Mathematics
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