Or perhaps you want to start in creative mode to build your home base and then switch to survival mode to take on the world from the comfort of your freshly built castle.
Minecraft lends itself to creativity and changing playstyles, however, and you may find that the map you intended to make a creative map feels like it would be a perfect survival map or vice versa. Under normal circumstances this selection is fixed and a permanent flag is set within the world file.
You can choose from creative, survival, and hardcore modes. When you create a new world you select your game mode.