Robert MacPherson explores fundamental aspects of the meaning and making of art. His approach almost always involves the use of multiples, a sequence of similar or identical objects. This associates the works with a convention in later twentieth-century art of making what are known as 'serial' works, which imply a continuum rather than presenting a single object as an isolated phenomenon. In Paddy's gale: 22 frog poems for P.L., the continuity suggested by serial, repeatable units, indicates that this particular work is a detail within a much wider system, a complex grid of interlocking factors which defines the meaning and identity of things.

As well as this abstract and philosophical character, MacPherson's work also embodies deliberately basic humour, not to debunk serious art, but to endorse the richness and interest of ordinary life. Many of his works are described as 'Frog poems' and there is a very human pathos in combining the romantic connotations of poetry with the endearing, but ugly frog.

In Paddy's gale: 22 frog poems in P.L., the waterbags are a pun, at various levels, on the familar idea of art on canvas. Being painted canvasses hanging on the wall they make the identity of paintings ambiguous. As containers, the bags are an ironic allusion to the notion of content in art. Each bag has a letter stencilled on the side, making the Latin name of a species of frog 'Cyclorana Platycephalus' (this is in fact a burrowing frog which, like the bags, stores a large reserve supply of water inside itself). The appearance of the bags, with bulbous bellies and two steel rings like round eyes where the handle attaches to the bag, is also reminiscent of the appearance of a frog. This process whereby the meaning of something is built up through the accumulation of diverse associations, some banal, some esoteric, is a particular concern of the artist.

MacPherson regularly uses the classification and scientific naming of frog species as an analogy for language and the naming of things. Generally he finds and highlights a disjunction between the ordered system of language and the world's chaotic plethora of things that language describes. With ironic humour this work evokes and analyses the way in which paintings attempt to create a logical picture of the world.