The Argumentum ad Futuris, or Appeal to the Future

Although the argumentum ad hominem is often discussed in logic textbooks, the argumentum ad futuris, or appeal to the future, is seldom mentioned. Indeed, I can find only one brief discussion of the ad futuris, and that discussion treats the argument only in its fallacious mode. Presumably, however, as with the ad hominem, not all instances of the ad futuris are fallacious. In this post, I want to discuss the basic form of the ad futuris, look at some specific examples, and then try to formalize the argument and distinguish between its fallacious and non-fallacious versions.

What is the ad futuris?

In its basic form, the ad futuris is an appeal to potential future evidence, culminating in the claim that this evidence will both vindicate the truth of some proposition p and show the falsity of p's negation. For example:

Pat: There is no evidence of extraterrestrial life, so I suspect that there isn't any.

Jamie: Oh but surely we'll find evidence of extraterrestrial life in the future. The universe is so large that there is bound to be life out there, and we just need time to find it--or for it to find us.

Jamie’s implicit claim is that the truth of Pat’s proposition is dubious given the likelihood of future evidence against it. If Jamie is right, then we should not assent to Pat’s claim that there is no extraterrestrial life. A slightly more complex version of the ad futuris occurs when a theory makes a claim that isn't currently supported by the evidence:

Pat: Your theory makes this particular claim, but there is no evidence for it.

Jamie: True, but there isn’t a lot of data about that particular issue, and my theory still has more explanatory power than competing theories. I suspect that future data will provide evidence for this particular claim.

Jamie's point here is that it's rational to believe that future evidence will vindicate the claim in question and that we should still accept the theory that generates the as yet supported claim.

Specific Examples of the ad Futuris

An example of Jamie's reasoning occurs in Origin of Species:

That our palaeontological collections are very imperfect, is admitted by every one. . . . Only a small portion of the surface of the earth has been geologically explored, and no part with sufficient care, as the important discoveries made every year in Europe prove.

In addressing the paucity of transition forms in contemporary fossil collections, Darwin points to their incompleteness and notes how little of the earth had been explored. Presumably, collections would improve and provide more evidence for Darwin's views on transition forms.

Another example of the ad futuris occurs in response to John Searle's Chinese room argument, which argues that computers do not and cannot think. One response to Searle is that computers in the future will be able to think. For example, Ray Kurzweil writes:

[A]s for computers of the future that have the same complexity, depth, subtlety, and capabilities as humans, I don’t think we can rule out the possibility that they are conscious.

Moreover:

[H]umans are unable to directly transfer their knowledge to other persons. Computers, however, can share their knowledge very quickly. . . . Thus future machines will be able to combine human intellectual and creative strengths with machine strengths. When one machine learns a skill or gains an insight, it will be able to share that knowledge instantly with billions of other machines.

Kurzweil argues here that advances in computing will show that Searle's claim that computers cannot think is false and that it's reasonable to believe that future computers will have properties far more advanced than current computers.

The Form of the ad futuris

Because an appeal to future evidence cannot guarantee the truth of the claim in dispute, the ad futuris is an inductive argument. If the premises are true, then the conclusion is more likely to be true than not. Here's one way to formalize the ad futuris:

1. The claim that p is the case is not currently supported by evidence.
2. It is highly likely that evidence supporting that p is the case will be found in the foreseeable future.
3. Therefore, p is the case.

The second premise does most of the argument's work. The phrase "highly likely" or its equivalent is necessary if the argument is to be inductively strong, that is, it must be more likely than not that future evidence will support that p is the case. The crucial feature of a non-fallacious ad futuris is that it provides good reasons for thinking that future evidence in favor of p will emerge. Thus, a fallacious version of the ad futuris merely appeals to future evidence without explaining why it is likely that future evidence will show that p is the case.

The phrase "foreseeable future" or its equivalent is important because an appeal to the distant future undermines the claim that we currently have good reasons for thinking that future evidence in favor of p will emerge. An appeal to a distant future merely postpones doubts about the truth of a claim based on some hypothetical time that supposedly will vindicate the claim. Hence, an ad futuris based on an appeal to a distant future is fallacious.

An ad futuris is also fallacious if current evidence tends to cast doubt on the claim that p is the case, because opposing evidence decreases the likelihood that future evidence will support p. Again, a good ad futuris provides reasons for thinking that the absence of positive evidence is temporary. Appealing to future evidence in the face of contrary evidence is special pleading.

Finally, a more sophisticated version of the ad futuris can incorporate non-evidential reasons for accepting that p is the case. For example, if a theory generates claims X, Y, and Z such that X and Y are well-supported but Z is not, one can appeal to the explanatory merits of the theory as well as the strong likelihood of future evidence for Z. In other words, inference to the best explanation can be incorporated into an ad futuris:

1. The claim that p is the case is not currently supported by evidence.
2. It is highly likely that evidence supporting that p is the case will be found in the foreseeable future.
3. The theory that generates p is otherwise well-supported and is superior to its rivals.
4. Therefore, p is the case.

In this version of the ad futuris, the likelihood that p is the case is bolstered by both foreseeable evidence and the explanatory superiority of the theory that generates it.

Further Reading

"Chinese Room Argument." Internet Encyclopedia of Philosophy.

Norman Geisler. Come Let Us Reason: An Introduction to Logical Thinking.

Ray Kurzweil. Are We Spiritual Machines? Chapter 6: Locked in his Chinese Room: Response to John Searle.