by themselves

by (oneself)

1. Alone. Because there's usually so much going on with the kids, I really enjoy spending a quiet Saturday night by myself.
2. Through one's own efforts alone. You can't move that table all by yourself! Here, let me help you. My little girl loves to get dressed by herself, so tutus and cowboy boots have become the norm around here.
See also: by
Farlex Dictionary of Idioms.

by themselves

 
1. with help from no one else. Do you think they can do it by themselves? Mike and Max cannot lift the piano by themselves.
2. with no one else present; alone (of two or more people). They are sitting there by themselves. Let's sit with them. They enjoy spending the evening at home by themselves.
See also: by, themselves
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • at will
  • at the end of (one's) fingertips
  • be hoist by (one's) own petard
  • be hoist with (one's) own petard
  • be hoist with one's own petard
  • be hoist/hoisted by/with your own petard
  • be on (one's) pat
  • at (one's) doorstep
  • at doorstep
  • a ball and chain
References in classic literature
"Say you so?" says the other Spaniard; "such things are not to be slighted, I assure you; there is certainly some mischief working near us;" and presently he asked him, "Where are the Englishmen?" "They are all in their huts," says he, "safe enough." It seems the Spaniards had kept possession of the main apartment, and had made a place for the three Englishmen, who, since their last mutiny, were always quartered by themselves, and could not come at the rest.
Within these virtual circles, teens become part of what they regard as a cool Internet practice and, at the same time, intensify feelings of being connected to friends, even when sitting by themselves doing homework, Kraut says.
* activities that provide opportunities for children to participate in large groups, small groups, with partners, or by themselves;
Despite the fact that the Portuguese lyrics probably were incomprehensible to most in the audience, Ribeiro allowed these excellent musicians to perform by themselves at various points in the program.
It is simply that, by themselves, they cannot account for the aesthetic success of these paintings.
There's something deeply subversive, however, in the notion that individuals might actually be trusted to cope by themselves with the hazards to be found in their file cabinets and laser printers.
Here is where culture gurus Kennedy and Deal finally put their money: face-to-face communication between people who want to participate in meaningful work and achieve larger objectives than they could by themselves.
owner, Waller discovered franchising allows owners to be in business for themselves, but not by themselves. Franchisees have the advantage of using a proven system and leaning on a network of supporters who have a vested interest in the business' success.
Don't pull them out and put them in schools by themselves. Schools for women simply don't make sense.
Participants then viewed videotapes of these sessions by themselves in separate cubicles.