Probably a dozen or so, and there's no "one sentence" reason for that being so.
First off, there are no knife shops in my area, where I could go and actually hold a knife in my hands before purchasing,,,, every knife has been bought "on-line". Returns were not always an option or even a consideration, given re-stocking fees and shipping costs involved. Over all these years, there's only one knife that I've actually returned because I hated the edge so much.
Second, I tend to buy knives according to their category,,, for example "paring knives". Some are spear-point, some are sheep's foot, some are bird's beak, some are too long, some are too short, and I end up with multiples, and I tend to settle on one knife that I use for most everything that particular category requires. I find most paring knives "too long". The paring knife I use most, was my girlfriends' knife, bought in a yard sale maybe 40 years ago. The tip was shot due to it being used as a screw-driver,,, so I cut the tip off, and re-profiled it as a 3" sheep's-foot, and I may keep using that terribly re-curve-bladed knife with a badly worn handle, until the day they put me in a box.
Petty/utility/sandwich knives is another category where I've bought multiple lengths, and multiple geometries, looking for that one knife that suits me best. Some of those are more along the lines of carver/slicers,,,, some more closely resemble a short "chef's knife",,, some have different handles, etc. Lengths range from 4.25" to 4.5", to 5", to 5.25", to 5.5", 5.75", 6", 6.25". My preferred choice ended up being a 6.25" carver-slicer type petty, because it clearly offered the greatest versatility for my style and everyday use. Ease of maintenance was another factor.
Chef's knives was another category, and since I'm a senior, and these days I'm cooking for "one", I seldom if ever need to use a larger chef's knife, yet I have knives ranging from 7", 8" 10" and 12". I've been buying knives for over 50 years, so it's easy to see why I may have acquired so many over that lengthy time period.
Then there's the cleavers, of which I have roughly three,,, maybe four,,, a few 10" bread knives,,, and several specialty knives,,, most of which I may never use, simply because my own needs today, no longer require it.
Others I haven't mentioned are long slicers (10" plus),,, boning knives,,, fillet knives, "rocking" knives". presentation carving sets, etc. It adds up over time.
Most of my knives are German (Zwilling Pro S, and Pro), Wusthof Ikon and Classic, Victorinox Rosewood series. My Japanese knives are by MAC, Shun, and Miyabi.
I have zero intention of ever becoming a collector, yet I can readily understand why so many folks do. I have a deep respect for the tradition and workmanship behind so many beautiful Japanese knives, but at this stage of my life, I'll simply have to be content viewing them from afar. That said,,, I just may buy "one" more,,,, only one.
