In both the natural world and human society, there are many circumstances where the deliberate but passive withholding of information can confer an advantage. Nocturnal species attempt to keep the knowledge of their existence secret from all those predators that are active during the day. Guarding the password to a bank account confers the advantage of not being robbed. Keeping the location of a threatened species out of the public domain, accords that species some protection from extinction. By not revealing previous ethnic, political, military or religious allegiances, refugees and war-criminals may gain the advantage of sanctuary in exile. Behind every locked and windowless door there is knowledge of abuse, hoarded treasure, sacrifice, love, shame and death, that is kept a passive secret from the world of public inquiry.

All unique uncommunicated pieces of information are not secrets. Every conscious moment, every individual has the ability to store large amounts of information that is unique to themselves and is never communicated to others. Very few of them will end up as secrets. Most individuals can probably remember when they last ate food, drank, passed urine or defecated, but for the most part, such knowledge is neither secret nor public. When an enthusiastic gardener discovers worms in the compost, the knowledge does not become a secret when s/he doesn't bother to tell anybody. Just because I didn't give you my contact number, there is no need to assume that it is secret. I forgot.

All knowledge treated as secret has a shelf-life. The secrecy of a pregnancy has an expiry date that varies according to the abilities of the interested parties. The hidden cache of acorns squirrelled away for a rainy day, will germinate into an oak tree at the beginning of next season. The date of a surprise attack expires the moment of the invasion. Even skeletal remains hidden in a cupboard will eventually be obliterated by natural disasters, development and social evolution.

As the stakes become higher, the need for secrecy become more significant, and the recourse to deception more probable. The larger the stash of loot is, the more impenetrable does the security system need to be. The bigger the military operation intended, the more carefully does the plan of action need to be hidden. Citizens need to keep their opinions secret in the face of powerful totalitarian political control, because unearthed secrets such as these, tend either to invoke some sort of bullet from someone else's gun, or an exile trip to the silicon mines of Mars.

Deception becomes necessary, when active strategies are involved in sustaining the secret. Action that attempts to preserve a secret by manipulating uncritical expectations, inevitably morphs into deception. The bagmoth Liothula omnivora keeps its presence a secret from predators by a camouflage that blends into the local chaos of its environment. Fraudulent company directors deceive investors by not revealing the true financial state of the company. During periods of promoted moral standards, keeping the knowledge of an illegitimate birth secret from the righteous hypocrisy of the guardians... perhaps by means of false birth certificates for example... would be nothing more nor less than a pragmatic strategy. Whether to categorise such action as secrecy or deception will depend more on moral attitudes than philosophical analysis.