How can we justify basic research funding? Definitions: Basic science is research conducted without immediate applications in mind. It is driven by the "curiosity [...] to expand [humanity's] knowledge, not to create or invent something." Applied science, on the other hand, is conducted to "solve practical problems of the world, rather than acquire knowledge for knowledge's sake," or to "improve the human condition."

Edit (as per JeffE's suggestion): Let us define 'we' as academics, and 'to whom' as questioners ranging from grad students experienced with research, to sponsors familiar with research, and to the general public (friends, family, etc.) in fields outside of research.

Question: How can we justify funding for basic research? In other words, how can we justify maintaining the status quo for (or even increasing) the funding of research without immediate applications?

Why address this question?

Over the past 10 years internationally, funding in both the public and private sectors for basic research has been decreasing. In 2014, Canada cut funding for basic science in 2014* to "place a new emphasis on applied research."

Likewise, Austrian researchers reported in 2011 of a popular opinion in their country "to [avoid investing] in costly basic research when the results of other countries’ basic research are [...] available without charge."

Finally, a 2014 article in Nature reported of basic funding cuts in favour of "a focus on applied research [...] in Argentina, Canada, Denmark, [France], Italy, Portugal, Russia, Senegal, Serbia, Spain, the United Kingdom and the United States."

Outside of shaping policy, addressing this question can inspire graduate students who may be doubting the usefulness of their research, create an informative resource for undergrads considering a career in basic research**, and provide meaningful answers when asked by the general public (friends, family, journalists, etc.).

Explanatory footnotes:

*More precisely, the CIHR (Canadian Institute of Health and Research) reduced funding as Canada's "federal funding body for biomedical research." Another source by the CAUT (Canadian Association of University Teachers) reported that "federal support for basic research has slowed significantly over the past six years [2007-2013]."

**Interestingly, researchers of a study in The American Biology Teacher "designed an activity in which students take part in a mock grant panel [for disbursing funds for grant applications]. The results indicated a strong tendency toward student funding of applied medical research at the expense of basic research. Exposure to a few examples of important basic research moderates this tendency."
I split this answer into three sections by the type of source (peer-reviewed literature, Stack Exchange, and miscellaneous). Each source is followed by a quote and/or a short description.
I also included a summary of key takeaways at the end.
The Literature
Woods, N. N., Brooks, L. R. and Norman, G. R. (2005), The value of basic science in clinical diagnosis: creating coherence among signs and symptoms. Medical Education, 39: 107–112. doi:10.1111/j.1365-2929.2004.02036.x
This study investigated the relationship between basic science knowledge and skill in diagnosing relevant diseases. The researchers concluded the study by saying that:

[...] the study has shown that, in comparison with students who
learned conditional probabilities, students provided with a basic
science explanation for diagnostic categories were better able to
accurately diagnose cases after a delay.
A plausible explanation is
that the basic science information, because of its conceptual
coherence, was itself more memorable, and that it also provided a
means to reconstruct the features of individual disease categories
after the initial symptom lists had been forgotten.

Magne, F. (1993). Importance of basic research in applied phycology. Hydrobiologia, 260-261(1), 25-29. doi:10.1007/BF00048999
The section of the abstract below highlights what Magne views as the value of basic research in the applied study of algae (aka phycology).

It is noteworthy that [applied phycology] research can not avoid the
use of knowledge obtained by basic research; applied phycology is
especially indebted to basic research in adopting biotechnologies
which are typically coming from basic research.

Leander, C. A., &amp; Whitton, J. (2010). Bling my research! A mock grant panel activity illustrating the importance of basic research. The American Biology Teacher, 72(5), 308+.
In a classroom activity, the researchers demonstrated the importance of basic research to first-year undergrads. In describing their methods, the researchers said:

First, show the class a photograph of a cancer cell
labeled &quot;GFP.&quot; [...] Briefly
mention the leaps in understanding of cancer cell growth and cell
division that GFP has made possible. Introduce the students to [...] Osamu Shimomura, who [...] was hired to simply investigate why a dried jellyfish glowed
green when crushed. The resulting manuscript describing GFP gives no
hint to the future implications of this protein (Shimomura et al.,
1957), a discovery for which he would eventually share the Nobel Prize
in Chemistry in 2008.
Finally, [...] [m]ention the importance of sequencing in understanding
the evolution of HIV. [...] [I]ntroduce them to a profile of John Trela,
Alice Chien, and David Edgar, who discovered Taq polymerase during
basic research investigations. This discovery has earned billions of
dollars in royalties (Fore et al., 2006) yet was the unintentional
result of a basic research investigation into life at high
temperatures (Chien et al., 1976).

http://www.sjsu.edu/people/fred.prochaska/courses/ScWk170/s0/Basic-vs.-Applied-Research.pdf
Dr. George Smoot of the Lawrence Berkeley National Laboratory said:

People cannot foresee the future well enough to predict what's going
to develop from basic research. If we only did applied research, we
would still be making better spears.

Stack Exchange
Asked by biotech on Biology Stack Exchange: &quot;Why is knowledge of bacterial pathogenesis important?&quot;
Chris♦ wrote a brilliant answer in the link above. Below is an excerpt:

The contributions of basic research is the basis for applied research
and drug design. Without them, this wouldn't work. Besides that it is
also the curiosity of humans which drives science - without having any
particular application in mind. These often come much later.

An answer  relevant to this question on Academia Stack Exchange: &quot;How can a researcher improve his contribution to society?&quot;
User eykanal♦ said:

[T]ry to take to heart that basic research is directly useful to
society. Almost all modern pharmacology is based on decades of
fundamental biochemistry and biology research. Materials science is
based on years of basic chemistry and physics research. Basic math
research fuels advances in all types of engineering, from signal
processing to computational work to structural engineering.

In a comment, user Anonymous Mathematician responded:

I think it's important to frame things as eykanal suggests [...]
message should be &quot;basic research is of great value to society in the
long run, and here are some other things I do that have shorter-term
impact&quot;, rather than &quot;here are some things I do to make up for the
fact that my research sounds abstract and useless&quot;.

https://mathoverflow.net/questions/175847/how-does-one-justify-funding-for-mathematics-research
A sequence of compelling arguments in support of pure mathematics research can be found in the link above on Math Overflow.
Miscellaneous
http://www.icsu.org/publications/icsu-position-statements/value-scientific-research/the-value-of-basic-scientific-research-dec-2004
A statement by the International Council of Science said:

Whilst an exclusive focus on application may have some merit in the
short-term, there are several reasons why neglecting basic research is
seriously flawed in the longer-term:

Basic and applied science are a continuum. They are inter-dependent.
The integration of basic and applied research is crucial to
problem-solving, innovation and product development.

Skilled scientists with a good understanding of the basic theories and practice [are required for the] successful transfer of scientific
knowledge.

Excessive dependency on scientific progress in other countries is
rarely likely to lead to the resolution of local problems. Countries
need to be able to generate their own scientific knowledge and adapt
this to their own local context and needs.

The practice of science is increasingly international and the
research agenda is set by those who participate. A country with no
basic scientific research capacity effectively excludes itself from
having any real influence on the future directions of science.



A secondary source by the AAAS on an MIT report (the link to the primary source appears to be broken) states:

&quot;Basic research is often misunderstood, because it often seems to have
no immediate payoff,&quot; the MIT report says. &quot;Yet it was just such
federally funded research into the fundamental working of cells,
intensified beginning with the 'War on Cancer' in 1971, that led over
time to a growing arsenal of sophisticated new anticancer therapies —
19 new drugs approved by the U.S. Food and Drug Administration in the
past two years.&quot;
It adds, &quot;Do we want similar progress on Alzheimer's, which already
affects five million Americans, more than any single form of cancer?
Then we should expand research in neurobiology, brain chemistry and
the science of aging.&quot;

A very similar question to this on Quora asked, &quot;How do you explain the importance of basic/fundamental science to non-scientists?&quot;
The most compelling answer to me by Marc Srour is quoted below:

I assume someone who needs to have the importance of fundamental
science explained to them doesn't care much for the &quot;satisfying
curiosity and thirst for knowledge&quot; aspect of science (which, to me
anyway, is the dominant one), so I jump straight to practicalities.
[...] [Y]ou can't predict the road
that science will take. Even if you try to only do applied sciences,
fundamental research will be needed to develop new tools and
methodologies, or else you'll just be running around in circles and
never getting any new developments.

In extension of Srour's attitude of doing basic research for basic research's sake, I'd like to quote an interpretation of the views of physicist Richard Feynman in a review by Chris Toumey of the University of South Carolina. Here, Toumey wrote:

The reason for [Feynman] doing science is to satisfy a curiosity about nature. [...] Too few people, he complained, understood &quot;the emotions of awe,
wonder, delight and love which are evoked upon learning Nature's
ways…My lament is that a kind of intense beauty that I see given to me
by science, is seen by so few others&quot; (24 October 1967).
In a 1959 television interview, [Feynman said]: &quot;The reason that I do science…is…not the usual
motivation for helping human beings. The main motivation is the
curiosity and interest to find out about the world we're in&quot; (pages
419-420). He easily conceded, of course, that scientists see the
consequences of their work, but he adamantly bracketed their
motivations from the applications of that work which the rest of the
world experiences.


SUMMARY
The following is a bulleted list of key takeaways from the sources above.

Basic science knowledge is linked to better clinical diagnostic skills (aka diagnosing diseases) (Woods et al., 2005).
The investigation of &quot;why a dried jellyfish glowed green when crushed&quot; led to the discovery of GFP (green fluorescent protein), which led to &quot;leaps in understanding [cancer].&quot; Furthermore, &quot;a basic research investigation into life at high temperatures&quot; led to advancements in DNA sequencing. This directly led to further understanding of &quot;the evolution of HIV,&quot; earning &quot;billions of dollars in royalties&quot; (Leander &amp; Whitton, 2010).
Basic research is a necessity if we want to meaningfully continue advancements in applied research, especially drug discovery (Chris♦, 2015).
As stated by Stack Exchange user eykanal♦ (2014), &quot;Basic research is directly useful to society. Almost all modern pharmacology is based on decades of fundamental biochemistry and biology research. Materials science is based on years of basic chemistry and physics research. Basic math research fuels advances in all types of engineering.&quot;
According to the International Council of Science (2004), &quot;Excessive dependency on scientific progress in other countries is rarely likely to lead to the resolution of local problems.&quot; Furthermore, &quot;A country with no basic scientific research capacity effectively excludes itself from having any real influence on the future directions of science.&quot;
According to a 2015 MIT report, &quot;Basic research is often misunderstood [...] because it often seems to have no immediate payoff.&quot; However, the report contends it has directly led to the development of 19 new anticancer drugs over the past two years.
The report further says, &quot;Do we want similar progress on Alzheimer's, which already affects five million Americans, more than any single form of cancer? Then we should expand research in neurobiology, brain chemistry and the science of aging.&quot;
Basic research is beautiful. It's both intrinsically emotionally and intellectually stimulating; basic research for the sake of itself is rewarding unto itself.