Thing #36 gave us the distinction between semantic and episodic memory—both instances of declarative memory (sometimes also called ‘explicit’ although I think that conflates type of memory content with type of memory test). This is in contrast to procedural memory (“knowing how,” vs declarative’s “knowing that’), sometimes called ‘implicit’ (grrr). Skills (writing in cursive or riding a bicycle), conditioning (Thing #2 and #9), and priming (Thing #40) are examples of procedural memory.
Declarative learning tends to be preserved in amnesia. For example, Henry Molaison (H.M.) had severe anterograde amnesia (but only partial retrograde amnesia) following surgery to alleviate seizures, and thus was generally able to remember events from long before surgery but not able to form new long-term declarative memories. Nevertheless, he could learn new skills (e.g., mirror drawing, which improved with practice, even though H.M. reported each day of practice to be his first). Note that H.M. provides dissociations (Thing #44) between LTM and STM, and between declarative and procedural LTMs.
BTW: John Anderson’s influential ACT-R (Adaptive Control of Thought—Rational) model of cognition is built (in part) on the assumption that all knowledge is divided into irreducible procedural or declarative representations.
Also associated with this ‘thing’: Wilder Penfield and especially Brenda Milner and Suzanne Corkin worked with H.M. for decades to understand what he could teach us about memory. See, for example
Milner, B., Corkin, S., & Teuber, H. L. (1968). Further analysis of the hippocampal amnesic syndrome: 14-year follow-up study of H.M. Neuropsychologia, 6, 215–234 https://pdfs.semanticscholar.org/2dac/046a9303a568ed6253a7132a4e9194b6924c.pdf
ACT-R was overviewed in Anderson, J. R. (1996). ACT: A simple theory of complex cognition. American Psychologist, 51(4), 355-365. http://courses.csail.mit.edu/6.803/pdf/anderson.pdf
(Cognitive psychologists should at least know about Anderson’s ACT-R model, even if most of us don’t understand it.)
And on amnesia: Squire, L. R. (1981). Two forms of human amnesia: An analysis of forgetting. Journal of Neuroscience, 1(6), 635-640. http://www.jneurosci.org/content/jneuro/1/6/635.full.pdf