Primary Mouse Button

What is the Primary Mouse Button?

The primary mouse button is typically the left mouse button. Technically, it's the button that performs the primary operation, which is normally the mouse button under the index finger.

Computer mouses are supposed to be operated with your dominant hand. For a right-handed user, the mouse is placed at the right of the keyboard, and the index finger of the right hand is placed over the left mouse button. Because most users are right-handed, the primary mouse button is normally the left mouse button. However, a left-handed user may feel more comfortable placing the mouse on the left side instead, in which case they will have to configure their system to swap the functionality of left and right mouse buttons to match the position of their index finger.

When using this terminology, if the left button is the primary button, then the right button is the Secondary Mouse Button.

Switching mouse buttons should be a seamless experience. Although many tutorials will say "left button" to activate and "right button" to open the context menu, in most cases when you press a mouse button, the operating system doesn't actually tell the applications that it's the left or the right button, but instead says that it's the primary button, or will simply lie to the applications if the buttons are swapped and tell them "left" was pressed when it was the "right" button. In some cases, it's not the operating system lying, but a development tool, such as a game engine, which used the term "left button" for convenience and familiarity instead of "primary button" which can be confusing for inexperience developers entering the increasingly abstracted world of user-interface programming.

A similar situation occurs when you use a drawing tablet. When the stylus pen touches the surface of the tablet, the operating system will lie to applications and tell them that a mouse button has been pressed, even though you aren't operating a mouse. This layer of abstraction ensures applications work reasonably consistent even with different hardware and system configurations.