There are two parts to this question:
1) What is truth?
2) What is happiness?
Plato couldn't answer the first one, at least to his own satisfaction, and the second one is even more vague.
I'm really surprised by some of the shallow answers here; probably youngsters, and goals of only 24 hrs of happiness? Seems a little short-sighted to me, but if you live in a drug-induced fog, that would be a long time.
The Steppenwolf has answered these questions (see Sources) and I've drawn them out a little more in my Essay on my web site under "Articles."
The conundrum of the question of happiness revolves around whether you can "Know thyself." I've defined this also in my Essay, but it takes awhile to get through the definitions, so hang in there and you'll be rewarded.
I'll give a shorter version here, in case you're too lazy to go to the site.
Essay
... we must distinguish between “knowing” and having information. “Knowing” is having direct experience of reality, while “being informed,” is having definitions, descriptions, names and narratives. Knowing vs. being informed are direct antagonists of each other. Knowing is a process that begins in the visual processing of the right side of the brain and culminates in the unification of reality and the two brain hemispheres, while becoming informed takes place in the left side of the brain and culminates in the total separation of reality and the two hemispheres of the brain.
The left side of the brain breaks up the world into finite components and time sequences, and the other, the right side of the brain, focuses on the unity of things in the world. The left hemisphere is the intellectual, syllogistic logical faculty that we measure through IQ tests, which excels in communicating finite concrete ideas, in addition to the definitions and descriptions that makes up the technological processes (chemistry, mathematics).
But not everything in the world fits neatly into definitions, descriptions and linear logic. Therein lies the problem with predominantly left-brained people, and Western civilization in general, who try to use this faculty to communicate all realities. This problem is compounded by the ingrained belief of most people that information is knowledge. And worse when we try to understand ourselves.
“Know thyself,” they say. But what is real? What is the truth?
We perceive the world through our faculty of consciousness, i.e., we perceive thoughts, feelings, physical forces and objects through our consciousness. But consciousness exists apart from the things we are conscious of. We are aware of thoughts and feelings, but these were not generated “consciously.” Neither is consciousness an entity (as is usually taught).
We are also taught that “will” is a separate entity, but it is not, neither separate nor an entity. Consciousness and the will are opposite polarities (passive and active) of the same function. They are not really separate. They
are two parts of the same thing, so I shall heretofore refer to them as “consciousness/will,” or simply “C/W.” As two parts of the same thing, they act in concert together. But the will also exists apart from the functions it sanctions, initiates, selects, controls, or suppresses.
We have verbal and graphic thoughts, but we also have a “thought generator, that throws thoughts into the sphere of consciousness, but functions outside and independent of the will. This is the mind.
We also have feelings, emotions and sensations, but also a “feelings generator” (incorrectly labeled as our soul). The generator of thoughts, emotions, and sensations is one and the same. But we have no perception of its existence and activity. Something (this thing) is working outside our sphere of consciousness that is guiding our physiological, mental, sensual, and emotional functions. This hidden, subconscious, or unconscious agent is called the spirit, the psyche, or soul.
Most people describe themselves with their habitual pattern of thought and emotional responses to events. And too, most people identify themselves as the thought generator (their minds) and its contents (their beliefs).
This misunderstanding is responsible for the impossibility to “Know thyself.” I have already described a hidden aspect of our selves which we share with God. Our soul or spirit is intended to be shared by God, and carries a designed and specific function.
The consciousness/will, or C/W, are the indicators of ourselves. If I assign them to the essence of our being, then I am defining our Selves as functions instead of entities. It becomes clear then, that these faculties within us are really the essential expressions of who we are, made by God to serve a function in the world.
Without God in the picture, we are reduced to nothing—a lost and helplessly drifting vessel. We are that which perceives the mental and physical worlds, but is imperceptible itself; that which “will” changes, but cannot (or will not) be willed or influenced to change. We are not aware of it, but C/W is the means through which we are aware of and dominate the world—inner (mental) and outer.
The spirit is the generator of our thoughts and emotions and sensations, as well as the functional agent behind our physiological functions (heartbeat, respiratory, blood flow, etc.); these are the forms and force--- through which our living is conducted, but is not who we are, even though we mistakenly think so. The spirit (unconsciousness) is the storehouse of knowledge, but devoid of consciousness, is incapable of knowing this knowledge. Neither can it know itself or anything, even though it stores the knowledge of the universe. And herein is the crux of the problem.
The consciousness/will can know, but has no storehouse of information. The C/W can initiate changes in the spirit, but lacks the power to carry them out. It can know itself and can identify with the not-self.
The spirit cannot initiate changes in its activities, but it is receptive to change from influences proceeding from the will, suggestions and stimuli from the environment, provided it is exposed to these at the right time or in the proper manner.
The underlying causes of our problems in the world, then, is lack of knowledge of Self, and acting with lack of truth or knowledge. We identify with the modalities of the unconscious, the spirit, instead of the conscious will.
The consciousness/will can decide which thoughts, feelings, and actions will be acceptable, but cannot generate thoughts and feelings, and lacks the power to carry out the acts it indicates to take place. On the other hand, the spirit has the power to generate thoughts, feelings and actions, but cannot direct these. One of them knows and directs, but is uninformed, while the other is incapable of knowing and directing, yet it is the power "to do" in the world.
Power is not an attribute of the will. The concept of interpreting the inability to act as desired, as weakness of the will, is erroneous. Nothing is wrong with the driver, if the car breaks down.
Without some Divine hand or purpose connecting the C/W and the spirit, we can't know anything, are totally lost, and can't possibly act correctly. The car has no driver; it is empty.
Do you begin to see the Divine Plan? Without God guiding our spirit, we are designed to be lost. Why did God go to all of this trouble, creating us in His own image, if this were not so? This begins to answer several questions. Why did God create Man? What is Man's purpose according to God? How can God be everywhere at once, or listening to us all, and acting for us all -- at the same time? It is because His spirit, the One Spirit, indwells within each of us, as part of our creation. He is life. It is why He is everything, without which, we are nothing. If God created us only to worship Him, why not create just a simple instinct instead, like the lower animals?
Now, allow me to address some questions that organized religion confuses. The church tells us that God created man "to worship God." This would certainly command us to build more churches and go to church often (every minute?) and get to worshipping(all worthy goals and we all need spiritual fulfillment, but not the question. Sounds more like a stick the church uses). Why not just create worshipping robots? This would be a shallow God indeed, if that is His purpose. Or maybe we are an evolutionary process after all, that got started from a random coming together of materials, and for which there is no reason, purpose or goal.
Suppose just for this moment, that before the creation, God was alone. The essence of life is consciousness, but the essence of living is action. So God created the world, but He was still alone.
Science and physics tell us that matter & energy can neither be created nor destroyed, merely transformed or modified. So then, God modified the energy/matter and created the world to have experience. But in a different energy state, He cannot interact with His creation.
Within the context of having experience through the creation of the world, God created man in his own likeness—given the same kinds, but not the same amount of powers, so that He can come into the world as one with, or through His creation. We are part of the One Spirit, designed that way, for His purpose.
Before Man (notice the capital "M", because Man is part of God) had knowledge, and not merely information, God took up residence at the center of Man's being, from where He coordinates and unifies the activities of Man's spirit. Since all things are modifications of His energy, and occur within His infinite expanse, He is the underlying unity of all things. This unifying attribute (omnipresence) of the original state of energy/matter and consciousness manifests itself as the essential function of the Subjective Realm, His infinite capacity to conceive (omniscience) manifests itself in the subconscious, and His infinite capacity to carry out (omnipotence) what is conceived is manifested in the spirit.
Where God is able to interact and reside, at the foundation of Man's being, is the Subjective Realm. There really is no true corollary to God. But from the beginning of time we have asked the question, "Where is the mind?" Where is consciousness located?" The truth is that consciousness can traverse the various levels of material organization (how else could our very cells recognize a disease, and counter-act it), but its origin is at the Subjective Realm.
God takes up residence in the world at the center of Man's spirit wherein He acts, during Man's spiritual infancy to unify his/her subconscious, mental, and life support functions, and if man develops or opens the higher parts of the spirit, God then extends His unifying functions to the affairs of Man's life.
To tap into the Subjective Realm of our inner being will enable Man to go through the innumerable obstructions in life unassailed. At this level of energy/ matter is the source of "oneness" (omnipresence), power (omnipotence) and wisdom (omniscience). The establishment (return) of consciousness to this level lays the foundation for the manifestation of these three divine attributes in the life of Man. This is where miracles happen.
Man is made in the likeness of God for a purpose: if fully evolved, for serving as a vehicle for God's manifestation in the world. For what other reason are the higher parts of Man's spirit equipped with the attributes of God? Man's earthly existence is not for our own sake, or for our pleasure, or some stage in the process of evolution, but neither is it simply to worship God. The purpose of creation was to provide God with a vehicle for the self-conscious expression of His divinity in the world.
The goal of Man's life is to bring this function to the foreground of our lives so that God may manage the affairs of our personal and social lives. And not just on Sunday (when we should be "worshipping").
Religious imperialism, or imperialism using religion as a potent weapon to dictate laws and Commandments, is not the answer. Determining behavior through fear and guilt, like Freud's motivators, is very primitive and useless. And as long as one's behavior is determined by likes and dislikes, and in the quest for pleasure and avoidance of pain, we will find ourselves unable to embrace certain obligatory realities.
The Greeks understood chaos, not as disorder, but as the absence of things (structures) to be ordered. Our Person is what most people take as their identity—our mind and its contents (beliefs). It is a veritable ocean of contradictory and conflicting ideals and emotional patterns of behavior. Our lives are pure chaos—the essence of disunity. Our emotions are in conflict with our ideals. Our personal interests are often in conflict with those of others and the environment. We have many contradictory beliefs. We slam the door in God's face—his unity, his expression—can only exist beside disunity, rather than through unity, and can only be expressed through oneness.
The intellect, the faculty that mankind relies on predominantly to communicate reality to itself, creates its own reality, blocking and bolting the door in four ways: 1) It communicates, not reality, but symbols of it, 2) The intellect can establish the logical connection between things and ideas, but lacks the means of establishing whether the premise of the logical operation is true or false, and, 3) what it communicates is hearsay (it thinks verbally or phonetically)—we have definitions and descriptions of things, of God, of the spirit, of our Self, etc., but no direct experience of these things, and therefore, no real knowledge, and 4) Intellect hides the unity between things, and thus speaks to us of a world in which things seem to exist by and for themselves and are in intrinsic conflict for the majority of people do not have an alternative mental input.
To open the door to God's ability and divine expression we must establish an inner peace unknown to most of us. We cannot achieve inner peace if we are still caught up in our emotional conditioning. Few are able to reconcile the idea of exchanging pleasure for inner peace. The enslavement comes from the intellect which defines certain things as pleasurable, painful, etc. , when there are no such things. Pleasure and pain are not qualities in things but expressions of a person's conditioned state. If you believe that beauty and sweetness are attributes that reside in a person or thing that you are in love with, you will not be able to do without it. If you believe that liking or not liking, hurting or enjoying, represent the natural state of your spirit, then you will not be able to transcend these emotions. Man must learn to enjoy with the knowledge that pleasure is not a property of the object of enjoyment, but of one's conditioning. It is a super-imposition on one's natural state of peace.
We can find equal enjoyment in all things. Nothing is enjoyable in itself. We do not really need anything to enjoy life. It can and must proceed from our will. It is this inability to realize this truth that prevents people from transcending their "love" for things of the world, that they may acquire the powers of the spirit. It has to be this way, because divine power cannot be conferred on people who have no control over their emotions, or understanding of their Self.
The ultimate reason for establishing inner peace as the dominant emotional response in life is that the manifestation of our divine nature depends on it.
In spiritual philosophy, "unity" is the foundation of good. Unity is the working of all things in harmony with each other, working as one; nothing goes beyond the limits to violate itself and others. The basis of unity is in God, or the one energy/matter and consciousness shared by all things in the world, and in which they all have their being. The arch-principle, "disunity," is what we call "evil."
Since unity is negated by the fact of physical and mental separation, the unity is established by a web of inter-relationships and interdependence between all things: Divine Law. The establishment of consciousness at the highest level enables Man to live holistically and morally.
Events in our earthly lives exist for the sake of our spiritual development, and our spiritual powers exist for the sake of guaranteeing us success in the world. This is one of the most important expressions of Divine Law.
Although dormant within the spirit of Man, the indwelling God makes its dormancy felt as a vacuum that manifests as the urge to oneness. Only God dwelling in Man's spirit can unify Man with his/her environment and men with each other. It is a dormant function that must be awakened that God may accomplish His goals in the world.
Let the glory that is done in heaven be done on earth.
God does not give to Man the things he/she needs in the world (but Man may tap the indwelling God, and in harmony and unity, and maybe agreement, we may effect things), but has created a world in which all things proceed to their inevitable goal through a web of interrelationships: the Divine Law. The Divine Law is not a set of rules—moral or otherwise—but the understanding of the interrelationships and interdependence between things. The proper presentation of Divine Law is in an exposition of the relationships (complimentary, supplementary, interdependence, etc.) that each thing in the world has with all others, and to the whole. It sets forth the meaning and intent. "X" must be done because everything depends directly or indirectly on it, and it depends, ultimately, on everything.
Neither does God directly punish (not that he hasn't, or couldn't). In all areas of life, to violate Divine Law invokes Divine Justice, which follows the model of a death that follows from ingesting poison.
The will is by essence Man's endowment of freedom. This freedom was granted to man to enable him/her to transcend the lower blind impulses in favor of following the Law of God. Be careful not to confuse "acts of will," when in reality they are often acts born of desire (emotions).
Here we have defined reality where Plato could not. But in philosophy, one thing seems to always beg another. What is the reality of truth? To be justified in truth is not just a matter of living morally, but of establishing harmony between the activities of the interrelated parts of the whole; of being in total equilibrium with God and the Law of God. The truth concerning anything depends on the principle of relationship, e.g., it is okay if you kill as the only option for the purpose of self defense.
We have answered the question, "What is truth?" But the subject is more easily understood if the question is formatted as "what is the truth concerning "X?" This is because truth concerns itself with the proper function of things, their purpose, and the correct interaction with, and use of things. We can discard the use of the word as a synonym for honesty, which is a Western reduction of an abstract concept to a sensual level.
The world has been dominated by imperialists and oligarchs, who can only stay in power by blunting the enslaved's sense of justice. Fearing the uprising of the people they exploit, they teach us to "Leave it in the hands of God," and "Turn the other cheek," and "Give to Caesar what is to Caesar." Since when, and how did Caesar come to own what others worked for? It was one of the world's greatest imperialistic nations, Rome, which published the text in which it was said that Jesus said this.
If someone strikes you on the cheek, and steals your shirt, the whole world and God must stand up and say "NO!" If you can get away with such conduct, the entire social order must collapse. If man has so much sense to make this the law of the land, he has outdone God. Otherwise, we have come full circle, and must define all over, and ask the question again, "What is truth?"
From the novel "Steppenwolf," by Hermann Hesse, "Man is not by any means of fixed and enduring form. He is much more an experiment and a transition. He is nothing else than the narrow and perilous bridge between nature and spirit. His innermost destiny drives him on to the spirit and to God. His innermost longing draws him back to nature, the mother. Between the two forces his life hangs tremulous and irresolute.
"That man is not yet a finished creation but rather a challenge of the spirit; a distant possibility dreaded as much as it is desired; that the way towards it has only been covered for a very short distance and with terrible agonies and ecstasies even for those few for whom it is the scaffold today and the monument tomorrow—all this is the Steppenwolf.
"As for the way to true manhood, the way to the immortals, he has, it is true, an inkling of it and starts upon it now and then for a few hesitating steps and pays for them with much suffering and many pangs of loneliness. Unwilling to suffer all these sufferings and to die all these deaths, he shuts his eyes. He is resolved to forget that the desperate clinging to the self and the desperate clinging to life are the surest way to eternal death, while the power to die, to strip one's self naked, and the eternal surrender of one's self bring immortality with them."