**3. Imagination: conceptual combination and interpretation**

Conceptual combination refers to joining two or more concepts to generate a new idea [13]. It is believed to be the most wonderful merit of the human mind [14]. At the neurological level, conceptual combination is made possible because any neuron (concept) in human brains can be linked to many other neurons unconsciously or consciously. The meaning of an object or event is thus determined by its activation pattern, a created network, of neurons [15, 16].

In engineering, many innovative ideas were indeed conceived and created through conceptual combination. For example, the electrical bicycle is made possible by joining an electricity-powered mechanism and the manual bicycle. Personal computers originated from the idea that the traditional mainframe computer could be carried with you wherever you go, like a briefcase. The Blackberry phone was first conceived by joining of two concepts: cell phone with email [17]; mirrors were added to elevators as a means to distract people's attention from the slow speed of elevators [18]. In other areas such as language, new words and phrases are constantly created via a combination of already existing words [19, 20]. In reading comprehension, the meaning of a sentence is achieved by activation and the integration of different word meanings in a sentence so that a gist in the form of a proposition for the sentence, a macroproposition for the paragraph, and a situation model for the entire text could be derived [21, 22].

Chance or luck has always been considered an important element in creative achievement [23]. For example, Campbell's theory of blind variation, selection, and retention [24, 25] argues that random variation is the basic mechanism that organisms use to cope with an uncertain environment. For example, mutation is the major mechanism by which a virus adapts to harmful environmental factors. Humans are blessed with a brain that can perceive the environment, store learning and experiences, and retrieve the information from memory to help understand and solve new problems that arise in the present and future. By manipulating information in the brain, simulating possible environmental changes, or just letting the brain wander randomly, humans, unlike lower organisms, can think and plan their coping responses in advance. The way human brains work to create new knowledge is by a random combination of ideas in the brain. Ideas may automatically collide with each other by chance, and some patterns may emerge unexpectedly to shed light on the puzzled mind [24]. However, mere activation and association of previously stored information in the memory is not enough to generate original ideas from conceptual combination. Some novel ideas that are remote associates from other knowledge categories must be found to help one get out of a rut [26], and interpretations must be made to meaningfully link the concepts [27], either automatically or deliberately.

After reviewing extensive empirical evidence from psychological literature, Simonton [28] used the theory of constrained stochastic process to account for scientific creativity. He pointed out that the road to scientific discovery was filled with uncertainty and luck. Logics and systematic thinking do not provide much help. They are primarily useful after the discovery to provide proofs and explanations for the validity of the discovery. Based on his analysis, Simonton pointed out two factors that contributed to scientific discovery. The first is the domain knowledge of which each scientist can only sample a small portion as the target of the study. The second factor is the scientists who evaluate the existing knowledge in the field of their study and who then try to find new and useful knowledge via the combination of knowledge shared in their scientific community.

In the theory of constrained stochastic process, the random combination of ideas that leads to scientific discovery proceeds in two steps. One is ideation, which refers to the generation of possible ideas; the other is elaboration, which refers to further explanation and refinement of the ideas. Because scientists usually work on more than one project at a time, the cross-talk from these diverse projects may provide chances for novel reformulations and discoveries. Blind variations and combinations of existing knowledge are thus the brain's mechanisms to generate original ideas for different types of creativity [25].

Technological innovation is founded on scientific knowledge. The difference between technological innovation and scientific innovation is that the former is less constrained [28] because there usually exists numerous possible solutions to a technological problem. Empirical evidence shows that random variation and conceptual combination are crucial for the emergence of original technological solutions. For example, Zeng et al. [18] found that the remote association of concepts from different domains spawned more creative mash-up web service design ideas in information technology than were generated from intradomain mash-up web service design. It is thus proposed that conceptual combination is the simple heuristics to promote imagination and creativity in all four CDIO phases in technological innovation.
