Controversy is the meat of science. Cognitive psychologists are tossing around hypotheses about what they call multiple category-learning systems. This issue relates to tacit knowledge because the brain would appear to have a different operating system for tacit knowing (see implicit in the research literature) vs explicit learning. Another term for tacit is procedural; Zaki and Kleinschmidt argue in a recent paper that what seems to suggest this difference is actually caused by task complexity instead of indicating a need for some alternative brain structure. Now a new research study just published in Psychological Science (Feb 2014, V25 #2 pp.447-457) claims the opposite. Their research strengthens the view that procedural learning (giving rise to tacit knowledge) appears to be dissociated from processes exhibiting explicit learning.