Perspective is the way in which objects appear to the eye, based on their dimensions and the position of the eye relative to those objects.
Smaller objects appear to be in the distance and larger objects appear to be closer and in the foreground.
Linear perspective is based on the idea that all lines, eg walls, ceilings and floors etc will converge on a common point on the horizon (that is, the level of the viewer's eye).
The point of convergence is known as the vanishing point. Parallel lines, for example railway tracks, appear to meet at the vanishing point. Atmospheric perspective refers to the colour and value contrasts which show depth in landscapes.
Foreground objects are generally clearer with sharper contrast, whilst objects which are further away have less distinct contrast and may fade into the background or become indistinct dark areas.
Camille Pissarro, Place Du Carrousel Paris, 1900
Note how your eye is encouraged to more around this space, following the lines of the foliage and the buildings.
The vanishing point is justly almost mid centre (just slightly higher) at the the spire in the background.
The colour becomes more muted from the foreground to the background, creating atmospheric perspective, and this helps to lead us naturally to this point.
Continuance is the way in which objects are placed so that the eye moves in a particular direction/s until a dominant object is reached.
Perspective tends to successfully direct the viewer’s eye in a given direction.
In addition, the direction in which any figures in the artwork appear to be looking can cause a similar effect.
Note how the arrangement of the dancers and the teacher leads the eyes around this picture, moving to the right just above the centre of the picture and to the left across the bottom. This is because not only of the placement of the people in an oval shape, but also because of the way in which the dancers face the right until the right hand edge, and then the teacher's exposed foot faces the left, which draws us back in the other direction.
Edgar Degas, The Rehearsal, c.1879.
The focal point ( focus or centre of interest) is where the most important object or person in the picture is located or where the artist wants the viewer to look at first.
The focal point may be obvious because of its position (eg at the visual centre), relative size, brightness, contrast or shape.
Foreshortening is the visual effect or optical illusion that an object is shorter than it actually is because it is angled toward the viewer.
Foreshortening occurs when an object appears compressed when seen from a particular viewpoint, and the effect of perspective causes distortion.
The artist records the distortion that is seen by the eye when an object or figure is viewed at a distance or at an unusual angle.
It is a particularly effective artistic device, used to give the impression of three-dimensional volume and create drama in a picture.
A familiar example of foreshortening would be when you look down a long straight road lined with trees, the two edges of the road appear to move towards each other and the trees look smaller the further away they are.
Vincent Van Gogh, The Café Terrace on the Place du Forum, Arles, at Night, 1888
Melozzo, Fresco (upward forshortening)
Pablo Picasso, Maya with a Doll, 1938
In this work, Picasso plays with his latest artistic processing of space and colour.
The plastic* phase of figurative distortion is continued, while the characteristics of the face are pushed and remoulded, as though constructed from modelling clay.
As always, Picasso's sense of fun and humour surface - the doll has the real face, whereas that of the child is surreal, a beautiful juxtaposition.
Both heads are absurdly enlarged compared to the rest of the body.
The doll's eyes match Maya's outfit and Maya's match the doll's sailor's costume, and so the child is interchangeable with the doll.
Plastic arts are art forms which involve physical manipulation of a plastic medium by moulding or modeling such as sculpture or ceramics. The term has also been applied more broadly to all the visual (non-literary, non-musical) arts.