When asked why something happens or is, we use two kinds of explanations: causal and teleological. As a parenthesis, I can add that there is a third kind, used specifically in mathematics, an explanation based on pure logical inferences (remember Pythagoras’s theorem and its demonstration?)

Take the question “Why there are clouds in the sky?” The causal explanation goes into the physical properties of water, the conversion of sun’s energy into potential energy and aspects of Earth’s atmosphere.  The teleological explanation is of another kind: There are clouds so that we have rain to water the earth, such that the plants can grow and we can have food.

It is the same explanation that we find in Psalm 104 (103):

¹⁰ He makes springs pour water into the ravines;
it flows between the mountains.
¹¹ They give water to all the beasts of the field;
the wild donkeys quench their thirst.
¹² The birds of the sky nest by the waters;
they sing among the branches.
¹³ He waters the mountains from his upper chambers;
the land is satisfied by the fruit of his work.
¹⁴ He makes grass grow for the cattle,
and plants for people to cultivate—
bringing forth food from the earth:
¹⁵ wine that gladdens human hearts,
oil to make their faces shine,
and bread that sustains their hearts.
¹⁶ The trees of the Lord are well watered,
the cedars of Lebanon that he planted.
¹⁷ There the birds make their nests;
the stork has its home in the junipers.
¹⁸ The high mountains belong to the wild goats;
the crags are a refuge for the hyrax.

I am always touched by the great vision which this psalm provides us regarding God’s majestic creation and its purpose. The Orthodox Christians have the joy of hearing this psalm at every Vespers service.

But which explanation is valid, the causal or the teleological? I believe they are both valid.

It is natural and normal that we use teleological explanations when it comes to human activities or human technology. To the question: “Why are the car’s wheels round?” even an adult answer is “So that the car can move smoothly.” Why are the windows transparent? So that we can have light inside the house.

When it comes to nature, some people reject from onset teleological explanations, as they assume a purpose behind the natural world. The surprising discovery is that children favor teleological explanations.

If you think that the teleological explanation (“it is so such that …”) sounds childish, you are right! It is childish, but not in the sense of “naïve” or “stupid”. Psychologists discovered that children favor such teleological thinking. They tend to explain in terms of purposes, not causes.

Why do children think teleologically?

One explanation is that they acquire the teleological thinking from conversations with their parents. Remember the Red Hood story? The girl asks the wolf, “Why do you have such big ears?” and he answers, “So I can hear you better.” A little boy asks his father, “Why does the sun set?” and the father answers, “So that we can sleep and rest.” The explanation of children’s teleological thinking would then consist in the fact that the parents short circuit their answers, avoiding appeal to science and concepts which the child cannot understand.

Some scientists believe that this is simply a developmental stage, which must be left behind as the child grows and participates in the educational system.

Recent research shows that the origin of teleological thinking in children does not necessarily come from conversations with parents. In an article published in 2004, four specialist come to this conclusion. Here is the abstract:
Research indicates that young children, unlike adults, have a generalized tendency to view not only artifacts but also living and nonliving natural phenomena as existing for a purpose. To further understand this tendency’s origin, the authors explored parents’ propensity to invoke teleological explanation during explanatory conversations with their children. Over 2 weeks, Mexican-descent mothers were interviewed about question-answer exchanges with their preschool children. Analyses revealed that children asked more about biological and social phenomena than about artifacts or nonliving natural phenomena, with most questions ambiguous as to whether they were requests for causal or teleological explanations. In responding to these ambiguous questions, parents generally invoked causal rather than teleological explanations. The tendency to favor causal explanation was confirmed by analyses of transcripts from a longitudinal study of spontaneous speech in a father-son dyad. These results suggest that children’s bias toward teleological explanation does not straightforwardly derive from parent explanation.
You may read the whole article here: http://www.bu.edu/cdl/files/2013/08/2005_KelemenCallananCaslerPerez-Granados.pdf

Such findings suggest that teleological thinking is deeply ingrained in the human nature. We are built to think in this way. It is the way in which Christians see the world (and also all Abrahamic religions, although not necessarily other religions, as for example Hinduism).

Just as we derive knowledge observing the chains of cause and effect in nature, we also derive insight observing chains of purpose and facts supporting it.

One may present a chain of causal explanations as following:

The clouds form because the water from oceans or rivers evaporates and then condenses in the atmosphere.  

And the water evaporates because it receives energy from the sun.

And the sun produces energy because of the nuclear reactions in its core.

And the nuclear reactions occur because the enormous gravity forces squire the core and raises the its temperature to such a degree that reactions are triggered.

And the sun formed after the matter expelled by the big bang started to condense in galaxies and stars.

Usually science stops here, although some modern cosmological theories try to go a few steps further.

The chain of teleological explanations may go like this:

The clouds exist so they produce rain.

And the rain is provided so that it can sustain the earth’s living creatures.

And the living creatures are provided to form a favorable environment for humans who are created in the image and likeness of God.

And God created humans as an expression of His love and creative power.

Teleological chains stop with God, as we cannot have knowledge of God’s nature, although we can know his energies (works).

It is important to notice that teleological thinking about nature is not restrained to theology. I read books written by scientists who are declared atheists or agnostics, in which they state (not without some amazing) that life presents us with something new, which we do not find in the rest of the material world. Life is intimately linked to purpose. We see it everywhere, from the struggle for survival of individuals and species to the special conditions which made life possible. Even popular Hollywood movies like Jurassic Park noticed it. The characters exclaim in awe: Life always finds a way.

Cause and purpose are in no way contradictory. In human activities we use physical causes to achieve human purposes. We put the water on the stove and use the heat to boil an egg. Is the boiled egg a consequence of a cause (heat) or the finality of a purpose (to provide food)? In reality, cause and purpose co-exists.

We can extend this observation to the whole nature. Things have causes, but they also have purposes, divine purposes. There is no contradiction between them. The Bible itself, telling us the story of humankind and of Israel, shows us that God’s purposes are in most cases – by far – accomplished by natural causes, except when God intends a demonstration of his power and love for humankind.

Ultimately every explanation chain, causal or teleological, ends in God.

I am Alpha and Omega, the beginning and the end, the first and the last.