In their  work, What is Philosophy?, Deleuze and Guattari propose that philosophy is, and perhaps has always been, “the art of forming, inventing and fabricating concepts” (2). Indeed, the Oxford English Dictionary (OED) confirms that philosophical attachments to this word in English go back to 1561: 

“Meddlinge all beawties together, he shall make an vniuersall concept, and bringe the multitude of them to the vnitye of one alone.” 

Here, Sir Thomas Hoby translates Baldassare Castiglione’s Il Cortegiano, an influential Italian dialogue in which courtiers discuss the ideal gentleman of the High Renaissance (a quickly vanishing position of privilege in the war-torn Italy of the early sixteenth century). Although Hoby is not the first to use the word “concept” in English, his usage of it has the productive twist that Deleuze and Guattari emphasize. In quotation above, the concept is something made– by “meddlinge all beawties together.” The concept of beauty is built from this union, paradoxically universal and yet singular. Somehow the concept manages the laborious work of carrying multitudinous beawties across a threshold, into altogether new territory. Indeed, it does this work continually. As each new experience or instantiation of beauty arises, the work of the concept begins again.

Although other examples of this word early English usage invoke “concept” as something suspiciously falliable or vain, they share Hoby association of it with certain their anxieties about values, morality, and aesthetic concerns. Hoby’s translation directly invokes the term in its etymological sense — in classical Latin, concipere is “to take in and hold, to become pregnant.”

Deleuze and Guattari go on to describe the amicable relationship between the concept and the philosopher. They invoke the erotic nature of this friendship and it’s bizarre self-actualization. Deleuze rejects the concept as: “A general idea or notion.” 

, a universal; a mental representation of the essential or typical properties of something, considered without regard to the peculiar properties of any specific instance or example. Meaning that is realized by a word or expression.”

Philosophy is not a simple art of forming, inventing, or fabricating concepts, because concepts are not necessarily forms, discoveries, or products. More rigorously, philosophy is the discipline that involves creating concepts. The object of philosophy is to create concepts that are always new. 

Concepts are not waiting for us ready-made, like heavenly bodies. There is no heaven for concepts. They must be invented, fabricated, or rather created and would be nothing without their creator’s signature.

philosophers must distrust most those con­cepts they did not create themselves (Plato was fully aware of this, even though he taught the opposite)

Mathematicians, as mathematicians, have never waited for philosophers before reflecting on mathematics, nor artists before reflecting on painting or music. So long as their reflection belongs to their respective creation, it is a bad joke to say that this makes them philosophers

Concepts are generative devices, not merely metaphors or representations. Nor are they mental constructs abstracted from the material world. Concepts are vibrant and indeterminate, having one foot in the virtual and one in the actual. Concepts operate as both logical and ontological devices. There is no a priori logical ordering between concepts. Concepts emerge from aesthetic-political acts (de Freitas & Sinclair, 2017),

Deleuze and Guattari argue that “concepts are centers of vibrations” (WP 23).

In their introduction to D+G’s “What is philosophy?” Hugh Tomlinson and Graham Burchell argue that this book takes up arms for philosophy.

“a general notion, the immediate object of a thought,” 1550s, from Medieval Latin conceptum“draft, abstract,” in classical Latin “(a thing) conceived,” from concep-, past-participle stem of concipere “to take in and hold; become pregnant,” from con-, here probably an intensive prefix (see con-), + combining form of capere “to take,” from PIE root *kap- “to grasp.” 

OED issues

I. Senses relating to thought or understanding. 

3. An idea underlying or governing the design or content of a product, work of art, entertainment

 II. Senses relating to imagination, opinion, or disposition.

Archaic – a draft or rough copy of a letter, official document 

1479   Earl Rivers tr. Cordyal (Caxton) Ded.   Ony mocion to blotte or ruste the clernesse of our goostly vndrestanding stirring vs to vnmesurable feer, or ony other presumptueux sinistre, or vayne concept. 

Deleuze, G., & Guattari, F. (1994). What is philosophy? (H. Tomlinson & G. Burchell, Trans.). New York, NY: Columbia University Press. (Original work published 1991)