Found an interesting introductory piece on lateral and vertical thinking:
When trying to solve a problem, it is very important to consider alternate solutions instead of forging forward with the first decent idea. Picking one idea and proceeding until a solution is reached is called vertical thinking and this is the type of thinking that is most often taught in our schools. When thinking laterally, you continue to generate ideas even after a promising idea has been produced. A vertical thinker must always be moving usefully in some direction and must be correct at every step. A lateral thinker can wander in different directions to find creative solutions and often must be wrong in order to be right in the end. Lateral thinkers welcome and explore seemingly irrelevant facts or ideas, whereas vertical thinkers shut out all irrelevant data
Lateral Thinking: Creativity Step by Step – Edward de Bono
The first practical explanation of how creativity works, this results-oriented bestseller trains listeners to move beyond a “vertical” mode of thought to tap the potential of lateral thinking.