2002 Honda Accord Clutch problem

Clutch does not rise. When manually lifted and depressed half way it automatically descends and remains down. If clutch is pumped half way quickly we get some pressure; however, it doesn't stay pumped and will descend again if depressed half way. Have confirmed master cylinder is not leaking as well as clutch slave; however, clutch slave can be depressed manually. What could root cause be and can a distinction be made between whether or not it's the master cylinder or the slave or any other possible cause? Thanks.