call : 非正式用词，含义广泛，指用说话或呼叫的形式召唤。
- She called me over to where she was sitting.
- I keep the bedroom door open in case the children call (for) me in the night.
- I was called to an emergency meeting this morning.
- At school she was always being called into the headteacher's office.
summon : 正式用词，指官方或正式的召集，召集者具有权力或权威性。
- General Rattigan summoned reinforcements to help resist the attack.
- On 20 July, the town council was summoned to hear an emergency report on its finances.
- We were summoned to the headmaster's office.
send for : 作“召唤”解时，语气较随便，暗示委派一件工作。
- Do you think we should send for a doctor?
- His son found him and sent for help.
- She sent for the latest sales figures.