Before giving you a definition on Fuzzy Logic, I would like to give you an example that clearly shows how spectral qualities are . Then we see why scientists began to believe in spectral nature of our universe.

Hermaphroditism
You are 100% sure that you are a boy/girl, aren't you? Can you believe there are many real people who cannot be 100% sure about their gender, logically?

Assertion of 'being a hundred percent sure about something' is not of logical interest. While we conventionally are convinced of 'what we are,' it cannot change our biological situation, which can say exactly the opposite. It is the case in hermaphroditism.

"If abnormalities of cell division occur, a fetus with mosaicism may result. The baby may have both cells with 46 XY chromosomes and cells with 46 XX chromosomes. This condition has been called hermaphroditism (after the greek god Hermes and goddess Aphrodite) and it is one of many causes of intersex. Because both male (46-XY) and female (46-XX) cells exist within the same fetus, both male and female structures develop. ... Whenever you see an infant with both hypospadias and an undescended testis (cryptorchidism), you must consider the possibility of intersex."
source: http://www.meddean.luc.edu/lumen/MedEd/urology/hrmphdt.htm

Pseudohermaphroditism
"congenital condition in which a person has external genitalia of one sex and internal sex organs of the other sex."

True hermaphroditism
"True hermaphroditism is a rare disorder of intersexuality, which if not diagnosed in neonatal life, usually manifests during adolescence. True hermaphroditism refers to the presence of both testicular and ovarian tissue in the same individual. The external genitalia in these individuals may range from normal male to normal female, however, most phenotypic males have hypospadias. ... In infancy, genetic counseling and determination of the dominant phenotype are crucial to gender assignment and rearing."
source: http://cpmcnet.columbia.edu/news/review/archives/medrev_v3n2_0000.html

"The following conditions can produce ambiguous genitalia and hermaphroditism:
* congenital adrenal hyperplasia
* fetal exposure to sex hormones
* testicular feminization syndrome
* XY gonadal dysgenesis
* XY gonadal agenesis
* chromosomal abnormalities
···o cryptophthalmos
···o Smith-Lemli-Opitz
···o 4p syndrome
···o 13q syndrome"
source: http://www.nlm.nih.gov/medlineplus/ency/article/001669.htm

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Further readings:
Hermaphroditism
Pseudohermaphroditism
True Hermaphroditism (includes an interesting case)