Collage was a device used by Picasso and Braque (along with cubism) to try and get around the two tyrannies of painting namely
a) The Flat Painterly Surface
b) The restrictive Highbrow aura of prestige connected with specific media and materials.

Dadaism; which was a 'smelly' new anti-art movement highlighting the excesses of classical culture in the face of the realities of war adopted collage and photomontage giving them a different 'voice'. Hannah Hoch made political photomontages and the Dada group toyed with jarring juxtapositions of meaning in a number of media including collage but also performance, assembledge, drawing and found art. Advertisements for Dada activities or meeetings weere usually pr4sented as collages, thus collage traditionally and importantly has developed a strong political and advertising voice. Surrealists like Dali and ERnst invoked the association of random or collaged ideas in his painting. The 'spin off' of Historical Dadaism, Surrealism continued with collage as a means of expressing its voice. Max Ernst was key to this as he made books of cut and re-collaged woodblock prints with weird, dreamlike and eerie associations. Ernst even encorporated an all-seeing avatar (the birdman 'Loplop') who oversaw the creations of his unique surreal perspective where the tokenly unusual took the place of banal reality.
All this led people to view an interpretation of physical reality outside of the usual visual format and procedures. Artists like Robert Rauschenberg and Jasper Johns showed that just about everything in life can be COLLAGED  as they included readymades like beds and stuffed animals , flags, maps, along with paint, random papers, screenprints &c in a COMBINE or accumulation of references direct and indirect.  The eye of the artist can often see collages in nature (i.e. driftwood and leaves swirled on sand) and as the result of nature's effects on man-made things. (weathered billboards) when seen through the camera's eye. Tearing and weathering is all a borrowed tool of collage.

What then can we say about the possible elements of collage????  If we ignore the issue of MATERIALS in favour of a discussion of OPTIONAL APPROACHEs I think the creative challenge even opens wider. Here are some 'structural' questions to look at -  referring to modern collage's VOICE and PRACTICE.

1. How important is the collager's emphasis on FIGURATION (fractured or unfractured).  HIGH ____________________  LOW?
2. Is 'environment' (Mis-en-scene) developed or is space purposely conveyed as impersonal ?
3. Is the collage playing with the Gestalt (impact) of 3D in use of space and or raised elements or by stuck on objects.
4. What is made important by emphasis and what is necessarily given background status. What % is background. How does this work overall.?
5. Is the work colour based, human based or icon based. An icon can be architecture, a bolt, a bird (anything recognised as a universal form) Is there admixture.
6. How important is LINE?  close lines.... curves...... sightlines
7. How important is SYMMETRY (or assymetry) in the piece.?  A Balance of Nortgh-South   East-West  or Diagonal 'flow'?
8. Is there a balance or symmetry of colour. Are the opposite colours used?  i.e. (red-green) (black-white)  (purple-yellow) (cyan-magenta)
10. Is it all monocolour (or monolcolour and a hint of colour?)
11,. Is the voice of THINGS INFERRED STRONG ENOUGH???
12. How important is the philosophy of experimentation... is a format of size or 'only taditional elements' asdhered to?
13. Are edges blocky, ripped , assymetrical, jarring, blended??????
14. Is there non-paper elements here  (on canvas, assembledge, mixed media?)
15. What design principles are invoked....
16. MESSAGE: What is being said?  Is it a message (include Title) DIRECT __________CONFUSED _______________ NEBULOUS____________.
17. SUBVERSIVE?????
18. Is the element of RETRO part of the voice. Is it a time piece evoking HISTORY.??
19. Is it imitating a natural collage of nature's elements.
20. Will it convey significant form and meaning to 'OTHERS'.
21. BUT MOST IMPORTANTLY  - AM I HAPPY WITH IT?

Hope this fuels some fresh thought and passion for artists!