There are four basic motions:

1. Main

2. Subsidiary

3. Privileged

4. Incidental

Main Motion

main motion is a motion that brings business before the assembly.  Main motions are made while no other motion is pending. While a main motion is pending a subsidiary, privileged and incidental motion may be presented; which will in many cases affect the assembly's consideration of the main motion. 

Subsidiary Motion

subsidiary motion is a type of motion that is dealt with by the deliberative assembly and is directly related to a main motion, but is taken into consideration before, or instead of, voting on the main motion itself.

Robert's Rules of Order Newly Revised (RONR)

Robert's Rules of Order recognizes seven subsidiary motions. Ranked lowest to highest in order of precedence, they are the motions to:

  1. Postpone Indefinitely-- to end consideration of the main motion for the balance of that session, without a direct vote on the main motion.

  2. Amend-- to change the main motion. (May also be applied to certain other motions).

  3. Commit or Refer-- to send the main motion and any pending subsidiary motions to a committee for consideration.

  4. Postpone to a certain time(or Postpone Definitely, or Postpone) -- to delay consideration of the main motion and any pending subsidiary motions.

  5. Limit or extend limits of debate-- to change limitations on number or length of speeches from those previously adopted.

  6. Previous Question-- to close debate, preclude any further amendments and vote immediately. (May apply to any motion or pending series of motions.)

  7. Lay on the Table(or Table) -- to suspend consideration of the main motion and any pending subsidiary motions to allow for immediate consideration of more urgent business.

Motions 1, 2, 3 and 4 are debatable and require a majority vote for adoption. Motions 5 and 6 are undebatable and require a two-thirds vote for adoption. Motion 7 is undebatable and requires a majority vote for adoption. Each subsidiary motion ranks higher than the main motion and lower than the privileged motions, and also yields to applicable incidental motions. (wikipedia 10/11)

Privileged Motions

privileged motion is granted precedence over ordinary business because it concerns matters of great importance or urgency. Such motions are not debatable, although in case of questions of privilege, the chair may feel the need to elicit relevant facts from members.

Robert's Rules of Order Newly Revised (RONR)

According to Robert's Rules of Order privileged motions are in order of precedence, as follows:

  1. Fix the time to which to adjourn -- if another question is pending.
  2. Adjourn -- but not if qualified or if adjournment would dissolve the assembly.
  3. Take a recess -- if another question is pending.
  4. Raise a question of privilege.
  5. Call for orders of the day.

Incidental Motion

An incidental motion relates to the main motion, as well as other motions, to varying extents.

  Robert's Rules of Order Newly Revised (RONR)

According to Robert's Rules of Order lists the following motions as part of this category:

1. Appeal the decision of the chair

2. Consideration by paragraph or seriatim

3. Division of a question

4. Division of the assembly

5. Objection to the consideration of a question

6. Parliamentary inquiry

7. Point of information

8. Point of order

9. Request for permission to withdraw or modify a motion

10. Suspend the rules

*Most incidental motions are undebatable.