What is the purpose of a film trailer?

There are multiple elements to a film's marketing campaign, whether it be the trailer, posters, advertisements or even viral marketing. These all contribute towards raising audience awareness through continuous exposure, as well as their interest in a film, in advance and during its cinema release. If audiences didn't have access to these marketing campaigns, they could possible have misconceptions and incorrect expectations of a film, a poster complimenting the trailer can reassure them.

The title of a film can also lead to incorrect assumptions, as it could potentially allude to a completely different genre and the overall atmosphere/pace of a film. Example of this include Dark Shadows, my first impressions of this title is that the film follows a dark genre - perhaps 'Horror' or 'Mystery'. I have made this assumption based on the conotations associated with "dark" and "shadows", as this could imply that something is unseen, creepy, threatening; all elements empahasised in horror films such as Paronormal Activity, The Cabin in the Woods e.t.c.

I could also use the film John Carter as an example, my initial impression is of a lifestory, a film focusing on an individuals journey due to the title consisting of someone's name - this emphasises the main character and subsequently puts the focus on them. Another reason behind me making this assumption could be because of my familiarity with films where the title follows the same format, such as Forrest Gump, Juno and Donnie Darko. However the latter wasn't so much a family drama conveying an individual's journey, as it was a fantasy/sci-fi drama, meaning that this film could have multiple inter-related genres, though without further information I am unable to guarantee this.

Finally, my first impression of Skyfall is that it has a sci-fi genre due the association of sky and space, something falling from the "sky" out of "space". Although it could  also follow and "end of the world" scenerio as the world as we know it - the sky - is falling down. I made this assumption as films such as 2012 and The Day After Tomorrow depict the end of the world due to natural disasters (dramatic weather change in the "sky" is an indicator in both films). If this was a contemporary recent film, it would be relevant towards the 2012 period, due to the controversial theory that the world will come to end when the Mayan Calendar finishes on Sunday, December 23, 2012.