When defining a term, there are three approaches which can be taken:

1. empirical-linguistic
2. lexical
3. stipulative

On the empirical-linguistic approach the term in question is studied as actually used by a sufficient number of people, or by people who have special knowledge or skills in the field concerned. From the synonyms and examples of usage, and from the contexts in which the term is employed one then derives (if possible) the objective meaning of this term for a particular speech community. On the lexical approach one consults a number of dictionaries and starts from the less subjective definition(s) given in these dictionaries which are left over after deleting those which are blatantly exclusivistic, supernaturalistic or obviously wrong for other reasons. (To take just one example: a traditional dictionary may seriously want the user to believe that death would also refer to what is unreal and untrue.) On the stipulative approach the term is defined in advance in order to make clear what one is talking about. Ideally, however, the empirical, lexical and stipulative definitions of a term ought to coincide so that no confusion can arise. And ideally, the term to be employed ought to have only one meaning, for homonyms are a notorious source of fallacious reasoning. Unfortunately, life and to a lesser extent also death and killing do not fulfil these conditions.

Etymologically life, to live and living belong together and we cannot accept any definition according to which the literal, original meaning of life is not related to what is characteristic of living beings. These 'living beings', in turn, must encompass at least all animal beings (including, for example, human beings) and all plants (including, for example, bacteria). It is now a question of stipulative definition whether things such as viruses are also living organisms, or merely complex protein molecules; or if not merely a question of stipulative definition, then a result of defining another term in a stipulative way. 'Life' is then the state of an organism with the capacity for reaction to stimuli and for metabolism and growth. A being which grows and which can reproduce itself independently is certainly a living being, but viruses which are capable of growth and multiplication only in the cells of other living beings may for this reason be said not to be individual, living beings. Consequently, if they are not counted as living beings for this reason, not any organism which needs, or still needs, an intimate bodily contact with a living individual can be considered a living being itself. This would not only apply to viruses but also, say, to spermatozoons and to fetuses if, and so long as, they need a womb or an artificial system maintained by human beings to grow and to keep growing. If it does not make a difference whether the organism needs a woman's or a man's body to survive and to grow, or whether this is all taken care of artificially outside anyone's body, then consistence requires that we forgo this criterion for all organisms from viruses, or the most simple organisms, to the most complex ones.

When we look at what characteristic quality, or set of qualities, living beings such as animals and plants have in common, our view of them is a nontemporal one in a loose sense. Strictly speaking of course, metabolism, growth and reproduction are temporal processes, yet given that a certain being has these capacities, it belongs to a species of living beings in the nontemporal (or not exclusively present) tense of to belong, unlike, for example, stones and minerals. On a temporal view, however, one individual is followed from its coming into existence, during its lifetime and until its death. Life then means something like period of existence of a living individual. Variants of this meaning are period between birth and death and the sequence of physical and/or mental experiences which make up the existence of an individual. In the temporal sense of living it is obvious that a living being need not be able to reproduce or multiply at all in order to be a living being, nor does it need to grow in the sense of getting taller or larger.

While the boundary between nontemporal life and death, that is, between living beings and dead things, is not sharp from an empirical-linguistic or lexical standpoint, the boundary between temporal life and death, that is, between an individual which is still living and an individual which has died, is not that sharp either. Some say that human beings in irreversible coma should be regarded as already dead. A patient may thus be declared "dead" if 'er brain has not been functioning for at least twenty-four hours (the body showing no response to stimuli, no general movements, no reflexes and an isoelectric electroencephalogram). The heart may then still beat spontaneously without the aid of a machine, something that is reason enough for others to call such a human being "still alive". Instead of irreversible loss of all electrical activity in the brain, irreversible loss of consciousness may also be held as a criterion of death. It has been said that death should be defined in terms of this absence of consciousness, since it would be from this alone that interest in the electrical activity derives. On the so-called 'double-test view' it is necessary that both all respiratory and circulatory activities have stopped and that the brain is so badly damaged that the loss of consciousness has become irreversible. This should guarantee that both the person and the body 'e had are dead. For a person may need a living body, but a living body certainly does not need a person.

What is important when choosing a definition or criterion is the consistence with which such a definition or criterion is applied: if the absence of all electrical activity in the brain is a criterion at the end of one's existence, it is also a criterion at the beginning of one's existence (here as a fetus of which the brain waves can already be monitored). As regards life in a nontemporal sense: if a spontaneous beating heart, or consciousness, were a prerequisite for being called "(still) living", beings which have no heart, or which are not conscious, would not be living beings. This would exclude plants, if not many animals as well, unless life and living are used in two different senses. What is also important is that the definition of what is 'life' or 'living' does not conceptually depend on some principle of life, or on any idea about the value or disvalue of life or nonlife. It is one thing to say that a person or 'er body is dead and quite another to say that 'er or its life is not worth preserving anymore.

Nonlife and death are the or a negation of life and as such privative concepts. What characterizes a nonliving or dead thing or body is the absence of any response to stimuli, metabolism, growth, reproduction and the capacity to move by itself, altho the absence of only one of these features is not enough per se to call a thing or body "nonliving" or "dead". As the negation of nontemporal life dead means nonliving (in a nontemporal sense), while as a negation of temporal life it means having died or not living anymore. Temporal death is only part of temporal nonlife, the negation of temporal life, because this negation also covers the period of preexistence, that is, the period before a living being came into existence. Furthermore, it also covers eternal nonexistence. (To define the temporal dead as not living as some dictionaries do, is therefore erroneous, when it means having died.) It is preexistence, life and death together which extend over the whole dimension of time. (Preexistence is not used here in the sense of eternal existence of the soul or person before the coming into being of 'er body, in which case not preexistence and death are complementary notions but preexistence and immortality.)

Neither temporal life and death nor nontemporal life and death are catenical concepts, even tho temporal life and death belong to a series of three concepts. Preexistence and death are not opposites, nor are life and death. Moreover, life, death and preexistence are not concepts which admit of degrees, or which do not admit of degrees while limiting concepts which do. (Altho it has been argued that life diminishes by degrees in a scale descending to death, it has never been pointed out what would be the unique catena or dimension involved.)

The temporal transition from life to nonlife or death is called "dying". Dying is to pass out of existence, that is, to pass from life in the case of living beings. When this transition is caused by a particular agency, people speak of "killing". What this agency is, may vary from a virus to a person, but in a moral context it is of course the question of persons killing living beings which is the focus of attention. It is not so obvious tho, whether the difference between causing the death of a living being and risking or allowing the death of such a being is of any moral significance. We must not delude ourselves into thinking that it is only killing which counts, and not risking or allowing death, or letting something or someone die. The fact that there is only a special word for causing death in the present language, and not for risking or allowing death, is merely a propositional fact with no bearing on the ground-facts. Similarly, it is only a propositional fact that there are no special words in the present language for causing, risking or allowing something to remain in a preexistent or potential state, but also here we must ask what the implications are of the difference between remaining in a preexistent state and having died; and what they are not.

Unlike killing, which refers to the mere fact of death caused by an agency in any manner, murder is said to imply full moral responsibility. Murder is not just a kind of killing which is bad, it is a kind of bad killing which is also intended and therefore wrong. When it is claimed that murder implies 'motive', it is intention which is meant, for people also speak of 'murder' when the motive is not someone's death but, for example, someone's valuables when these could only be obtained by killing the person in question. Such a motive is then probably a personal motive, but it can also be an impersonal one, while the killing itself remains deliberate. In such a case people tend to speak of "assassination". However, a political or military authority carrying out a death sentence would rather call it "an execution". It is precisely because murder has an inherent wrongness, and because 'everyone' is against murder, that people will employ every expression but the expression murder to describe their own deeds or those of their comrades. Only by seeing thru the emptiness and inconsistence of this verbalism can the plot of those playing this game of words be exposed. The substantive matters of life and death are just too serious to remain hidden between evaluative meanings and nebulous notions.