But, if you do, you will see more than seven, for several stars are tied for the status of seventh brightest star. Actually, and unlike almost all constellations, the Pleiades is a group of stars physically associated together in space, not just an accidental assemblage of near and far stars that appear together because they are seen in the same direction. The number will depend strongly on how bright the sky background is. Open clusters often contain a hundred or more stars, and this is true also of the Pleiades. With the naked eye, we see only the handful of most luminous members.
Most star clusters are too far away to be seen at all without binoculars or a telescope.
However, here in Taurus, there are TWO open clusters near enough for the unaided eye to discern individual stars. The second is the Hyades, in myth the daughters of Atlas and Aethra and, thus, half-sisters of the Pleiades. The Hyades are closer than the Pleiades and appear more dispersed in the sky. Incidentally, Aldebaran is not physically a member of the cluster but stands about half way between us and the Hyades cluster. Perhaps one of the fainter stars was once brighter.