Lat. distinguo, 1st person singular present indicative of the Latin verb distinguere, “to separate; to distinguish”.

Distinguo is a strategy developed in order to avoid a terminological difficulty or confusion, either perceived in the discourse of an opponent or envisioned in a polyphonical space as a possible mistake.
The word distinguo is also used as a synonym for paradiastole, S. Orientation Reversal.

1. Distinguo used as an analytical tool

Distinguos are useful for clarifying definitions of complex realities. In current language, to make a distinguo is to draw distinctions in order to clarify a complex notion.

The system of ‘territorial development’ is based on the interaction between its two components: the local economic system on the one hand, and the so-called ‘territorial’ system on the other.
The distinguo between the latter two systems stems from oppositions relating to the underlying logics that bear them. The economic system obeys principles that are recognized and exposed in economics. […] The territorial system, for its part, covers all the human, social, economic and urban functions of the place.
Lthe oinger & J.-C. Nemery, [Recomposition and development of territories], 1998.[1]

2. Distinguo used to rebut an argument

The distinguo is an instrument used to reduce ambiguity: “do not mix everything up!”. It can be used for example to detect a four terms paralogism , or, generally a shift in the meaning of a term in a reasoning. It is justified when it is based on socially recognized distinctions, independently established in a language dictionary or an encyclopedia, for example to eliminate the confusion created by the use of the word metal to refer to a chemically simple body as well as to an alloy.

In a second instance, distinguo is used to re-establish a blurred distinction (Mackenzie 1988). To make a distinguo is to say, “I distinguish [in your speech] some truth and some errors, and I’m going to rectify the mistakes”. Consider the following theological syllogism (after Chenique, 1975, p. 9):

Every man is a sinner
No sinner will enter heaven
No man will enter heaven.

The opponent says:

• • I agree with the minor proposition “every man is a sinner”.
  • In the major, “no sinner shall enter heaven”, distinguo, I distinguish two different statements:

— “(No sinner) as a sinner shall enter heaven”, I agree: “no man in a state of sin will enter heaven”;
— “(No sinner) as a forgiven sinner shall enter heaven”: I deny this proposition. The distinguo does not bear upon the meaning of the word sinner, but two categories of sinners.

(iii)     Therefore, I deny your conclusion.

The opponent therefore objects that the syllogism is fallacious, for the minor is true in one sense, and false in another.
This is not a case of a four terms syllogism fallacious by homonymy, S. Paralogism. Sinner is not ambiguous by homonymy, but because, it can be construed in two different ways in a theological context.

Distinguo is a figure traditionally dismissed as being “scholastic”, and used to draw spurious oppositions. Thomas Diafoirus courts Angélique, who hates him:

Angélique: — But the greatest mark of love is to submit to the will of her who is loved.
Thomas Diafoirus: — Distinguo, madam; in what does not have to do with possessing her, concedo; but in what does have to do with it, nego.
Molière, [The Imaginary Invalid], [1673][2]

Thomas Diafoirus is brutal and pedantic; he claims his right to possess Angélique, against her will; apart from this, however, he is ready to submit to her will. The distinguo is an instrument which prevents or rectifies ambiguities, but when it introduces distinctions into a perfectly clear expression, it can itself cause confusion.

In these cases, the distinguo may or may not be accepted according to the value of the distinction operated. In the case of the sinner, the distinguo might be justified by the parallel case of the criminal: a criminal having served his or her sentence cannot be called a criminal without qualification: one cannot say, “he is a criminal, let’s call the police!”, a distinguo is clearly necessary.
In the case of Angélique, the distinguo invokes an arbitrary, ad hoc distinction. In this case it can be countered by a third round of speech such as “stop it now!, enough with your scholastic distinguos!”, “stop quibbling please, you are obnoxious!”.

[1] Loinger G. & Nemery J.-C.. Recomposition et Développement des Territoires, Paris: L’Harmattan, 1998. P. 126.
[2] Molière, Le Malade imaginaire [1673], act II, scene 6. Quoted after Ch. Franks, D. Lettau, http://www.gutenberg.org/files/9070/9070-h/9070-h.htm (11-08-2017)