Alone on the island, the stir-crazy man had no choice but to soliloquize since there was no one else to talk to.

The play character would often soliloquize, talking to himself onstage instead of the other people.

The scientist tends to soliloquize and mumble to himself about the confusing parts of science that only he would understand.

With no friends, the homeless man tends to soliloquize, holding a conversation with himself since he had no one else to talk to.

The actor looked in the mirror and was able to soliloquize the speech eloquently even though he was only speaking to himself.