Abstract Concentrated slurry is known to exhibit shear thickening behavior, in which viscosity increases as the shear rate ascends. However, to identify the differences between this shear thickening behavior and rapid increases in viscosity (such as the dilatancy behavior of starch, sand, and other concentrated slurries) and the smooth increases in viscosity exhibited by concentrated slurries, this research investigated the rheological behavior of a polyethylene glycol suspension containing monodispersed silica particles with a size of 2.5 μm. The results found that the increases in viscosity as the shear rate ascends or the increases in elasticity as the strain ascends change consecutively from smooth and reversible behavior (i.e., continuous shear thickening (CST)) to rapid and irreversible behavior (i.e., discontinuous shear thickening (DST)) simply by increasing the concentration of the slurry, even in the case of concentrated slurries comprising of the same particles. DST is a manifestation of dilatancy in which a jamming transition occurs due to collisions between particles. Because CST transitions successively to DST, and the on-set shear stress of shear thickening of CST is almost the same with that of DST, shear thickening in the CST region may, therefore, also be regarded as the result of friction due to collisions between particles. This supports the research by Seto, Mari, Poon et al., which stated that shear thickening occurs due to friction from particle collisions.