John Baldessari's Tetrad series from 1999 is a profound exploration of thought representation through a unique combination of elements drawn from different sources. This series was presented in Baldessari's first exhibition with Marian Goodman Gallery and features four parts to each work. The pieces integrate imagery from film or video, artworks (notably by Goya), and everyday objects, along with excerpts of text from the Portuguese writer Fernando Pessoa. This amalgamation of visual and textual elements invites viewers into a complex dialogue between the seen and the unseen, the direct and the indirect​ (Marian Goodman Gallery)​.

The series, including works like "Tetrad Series: Real Shadows," employs ink-jet on canvas combined with acrylic and enamel paint, presenting a substantial scale of 94 x 94 inches overall. This choice of mixed media and large format further emphasizes the conceptual leap Baldessari encourages viewers to make from one piece of information to another, exploring the gaps and connections between image and text, between thought and expression​ (Marian Goodman)​​ (Marian Goodman)​.

Through the Tetrad series, Baldessari continues his investigation into the relationship between language and imagery, a hallmark of his artistic practice. The inclusion of text from Pessoa alongside the visual elements drawn from various sources underscores Baldessari's interest in the fluid interpretations of meaning and the viewer's active role in constructing narrative or conceptual bridges between disparate elements​ (Marian Goodman Gallery)​.