Why I can't use the time command in verbose mode without specifying the whole command path?

Given that... ~$ which time time is a shell keyword time is /usr/bin/time Why this works? ~$ /usr/bin/time --verbose ./some_script.sh Command being timed: "./some_script.sh" User time (seconds): 0.00 System time (seconds): 0.01 Percent of CPU this job got: 51% Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.03 Average shared text size (kbytes): 0 Average unshared data size (kbytes): 0 Average stack size (kbytes): 0 Average total size (kbytes): 0 Maximum resident set size (kbytes): 4572 Average resident set size (kbytes): 0 Major (requiring I/O) page faults: 1 Minor (reclaiming a frame) page faults: 1548 Voluntary context switches: 3 Involuntary context switches: 7 Swaps: 0 File system inputs: 48 File system outputs: 0 Socket messages sent: 0 Socket messages received: 0 Signals delivered: 0 Page size (bytes): 4096 Exit status: 0 And why this doesn't? ~$ time --verbose ./some_script.sh --verbose: no se encontró la orden real 0m0.124s user 0m0.101s sys 0m0.022s