Question 1: What is the name of the Formal Fallacy wherein a Deductive Conclusion is arrived at via the course of an Inductive Argument?

Question 2: Also, is this fallacy considered a "Deductive Fallacy" since it concludes Deductively; or rather, is it considered an "Inductive Fallacy" because its Form is Inductive?

This happens a lot, in linguistics, hermeneutics, philosophy, and religious discussions.

Argument Form:

  1. A is probably B
  2. B entails X
  3. Therefore, A must entail X

Example: Regarding Textual Primacy

  1. The Common spoken Language in Palestinian Israel, at the time of Jesus, was almost certainly Aramaic, or at the very least a Hebraic form of Aramaic.
  2. Jesus probably spoke his "messages" in Aramaic.
  3. Therefore, the most authoritative written/textual variants of the "Gospels" must be the Aramaic texts, rather than Greek.

(This argument precludes all kinds of other possibilities; but regardless, no matter how you dice it, no set of probable facts could entail certainty in this case.)

Specialization Example, "The Root Word Fallacy/Weak Analogy":

  1. In Greek, Similarity between words often times suggests the same meaning.
  2. The Greek word X is similar to Y
  3. Y implies Z.
  4. Therefore, X must imply Z.
  • 2
    The Argument Form is clearly not deductively valid; at most, you can conclude with : "Therefore, A is probably X". Commented May 30, 2015 at 9:28
  • Thank you. I understand that the form is not valid. I just don't know what to call the Fallacy. In contexts of Traditional Thought, Religion, and Hermeneutics, it is often the case that "Probabilities" evolve into "Certainties" -- in order to "break this pattern", it is often necessary, to show by clear and convincing evidence that this Error in Reasoning is actually, "A Thing", and people can go and look it up, to change their arguments. That is what I am trying to accomplish--the ability to point in the right direction. Commented May 30, 2015 at 22:41
  • ad probablyum :-) Commented May 31, 2015 at 16:14

3 Answers 3

  1. A is probably B
  2. B is X
  3. Therefore, A must be X

Is deductively invalid, so it would fall under the general fallacy type of invalid argument (assuming that it is presented as a deductive argument).

As an inductive argument, the "must" would make it fallacious on the grounds that the conclusion is not supported by the premises. However, I don't think anyone has named this exact form.

This variant:

  1. A is probably B
  2. B is X
  3. Therefore, A is X

For example:

  1. That animal is probably a frog.
  2. Frogs are amphibians.
  3. That animal is an amphibian.

Would be okay as an inductive argument-though its strength would depend on the probability that A is B. This seems to be similar to a statistical syllogism

  1. X% of As are B.
  2. This is an A
  3. This is a B.

For example: 1. 80% of humans have brown eyes. 2. Bill is human. 3. Bill has brown eyes.

  • 1
    Welcome to Philosophy.SE! "Would be okay as an inductive argument" ... not sure if I agree: if the animal is probably a frog but might otherwise be a salamander, then "That animal is an amphibian" would be true, but you haven't spelled out that extra premise. On the other hand, maybe it's a funny looking animal that looks like a frog but turns out to be a reptile, then (1) isn't enough to know that the animal is an amphibian. Commented Jun 1, 2015 at 22:38

What is the name of the fallacy

I'm not sure that this is a fallacy as such, but a problematic (where I am reading fallacy as being something that is always definitely wrong).

This happens a lot in linguistics, philosophy, and religion

Not only in those areas; it's just as true in the physical sciences, it's touched on in Hume most famously in the notion of causality in the physical sciences.

It's also true, in a different sense, in mathematics when a collection of results are placed in a deductive framework...they weren't discovered in this way; and one might place this in the broader picture of induction where induction is considered as part of the larger scientific episteme, or same.

  • Re "...placed in a ... framework...": true, and not just mathematically. Also made worse by the teaching of such frameworks as though they were historic or universal objects, i.e. the ancient discoverer of a particular modern framework's node X might be falsely inferred to be working from the modern framework's blueprint. In fields where the framework is even more complex than the history, benighted students suffer when once lively syllabuses are be mutated into stultifying specialist rote doctrines. Proposed name for the latter different sense fallacy: "the Publisher's Friend".
    – agc
    Commented Jan 30, 2017 at 15:59
  • Informal fallacies are definitely not defined as errors that are always definitely wrong. They are, generally, sometimes right. Commented Feb 8, 2017 at 16:40

Proposed Answer:

  1. A "Masquerade" is present when an argument's form consists of the bases for one type of argument - but is inconsistently presented as another form.
  2. The "Masquerade" facilitates the ability to present a stronger or weaker conclusion than is actually merited by the argument.

(If it is true that no "formal" name exists, or if "general fallacy" is insufficient.)


Deductive Masquerade Fallacy:

  • Premise A entails some plausibility or probability;
  • But inconsistently, Conclusion B is asserted deductively, despite non-deductive bases.

Example, Deductive Masquerade :

  • Spring began yesterday, and it rained yesterday.
  • Today, it is overcast, cloudy, and incredibly humid.
  • Therefore : It will certainly rain today.
  • (Rather: it will almost certainly rain today.)

Example: Inductive Masquerade

  • The government has a condemned housing buyback program.
  • Individuals in government are known to pursue conflicts of interest.
  • Therefore : It is highly probable that the buyback program also caters to a conflict of interest.
  • (Rather: It is plausible that the buyback program caters to a conflict of interest.)


The intent of the original question was to identify a "retort" which would efficiently communicate the objection raised--with the greatest economy of words.

I am not really sure if there is a "Formal" approach to publishing a proposed group of fallacies, but I hope this will help--if others happen to come across this dilemma.

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