Finding a Proper Definition of Deism
Deism, first, is essentially the view that God created the world but does not act supernaturally (or intentionally) in it in any way. It would be fair to illustrate God according to this definition as a sort of watchmaker, who creates and sets the dials in motion and then sits back to let it run. Deism, since it asserts that God cannot act supernaturally, denies the existence of miracles (e.g., as seen in the four gospels). For example, Thomas Jefferson (himself a deist), wrote a revised version of the gospels literally cutting out all of the miraculous passages, which later came to be called the “Jefferson Bible”. In the preface of the book, we see that “In 1803, while ‘overwhelmed with other business,’ Mr. Jefferson cut from the evangelists such passages as he believe would best present the ethical teachings of Jesus, and ‘arranged them, on the pages of a blank book, in a certain order of time and subject'” .
More interestingly is Diarmaid MacCulloch’s discussion on Deism in his book, Christianity: The First Three Thousand Years (2009) . He writes, “Between 1640 and 1700 a growing divide opened up between skepticism or openness on biblical matters among an educated and privileged minority, which parted with the passions of the Reformation… In place of the idea of the Tanakh and New Testament of a God intimately involved with his creation and providentially repeatedly intervening in it, there was a concept of God who had certainly created the world and set up its laws in structures understandable by human reason, but who after that allowed it to go its own way, precisely because reason was one of his chief gifts to humanity, and order a gift to his creation” . MacCulloch then says bluntly, “this was the approach to divinity known as deism” .
Joseph Addison (1672-1719) was an interesting Christian deist in the late 17th century. In inspiration given from Psalm 19, Addison expresses in the form of a poem the benevolence of God:
The spacious firmament on high,
With all the blue ethereal sky,
And spangled heavens, a shining frame
Their great Original proclaim.
Th’unwearied sun, from day to day,
Does his Creator’s powers display,
And publishers to every land
The work of an Almighty Hand.
Soon as the even shades prevail
The moon takes up the wondrous tale,
And nightly to the listening earth
Repeats the story of her birth;
With all the stars that round her burn
And all the planets in their turn,
Confirm the tidings as they roll,
And spread the truth from pole to pole.
What through in solemn silence all
Move round the dark terrestrial ball?
What through no real voice nor sound
Amid the radiant orbs be found?
In reason’s ear they all rejoice,
Forever singing as they shine,
“The hand that made us is divine.” 
To finish with an understanding in deism, it is also best to apply a few passing comments in regards to the relationship between revelation and reason from the deist perspective. Francis Schaeffer in his How Should We Then Live? (1976)  writes that the “Utopian dream of the Enlightenment can be summed up by five words: reason, nature, happiness, progress, and liberty. The humanistic elements which had risen during the Renaissance came to flood tide in the Enlightenment” . Apart from philosophical and theological changes taking place during the Enlightenment, more so significant political changes were taking place as well. Though matters of liberty and social reform were important subjects, they will of course not be discussed here .
Importantly however, reason over revelation was a significant defining point in Enlightenment secularism under the impression of separation from dogmatic authorities. In other words, though the early Enlightenment thinkers (especially the deists in particular) had a worldview based apart from divine revelation, they still yet maintained a religious connotation to themselves. As Geisler writes, “It is important to note that deism encourages a natural piety and worship of God(including prayer) as well as a strong emphasis on moral law. Indeed, one of the justifications of the American Revolution was the deistic belief that the moral laws of God are higher than the laws of man” .
This was an interesting point from that of Voltaire. As a deist, Voltaire had early on subscribed to the philosopher Gottfried Wilhelm Leibniz’s view that God could not have failed in creating the best of all possible worlds, (as seen in his work, Theodicy (1710)). However, Voltaire had come to later bring those views into question under a few circumstances regarding human suffering caused by natural and man-made disasters (the earthquake of 1755 in Lisbon produced his poem, Poéme sur le désastre de Lisbonne – “Poem on the Disaster of Lisbon” – which was a sign of his rejection towards Leibniz’s view).
However, before Voltaire’s change in perspective in regards to the human condition, one biographer notes that “he was still convinced that, on the whole, Newton’s eminently rational laws permitted human beings to accommodate themselves and seek their happiness within this orderly universe, set in motion by a supremely powerful but also benevolent being” . The important note of this point is to show the nature of Voltaire’s deism contrasted from that of a theistic point of view (since he has been confused as sometimes a theist or even an atheist). With this basic introduction to deism set in place, I do wish to make a quick examination as to the inconsistencies of the deist worldview.
The Inconsistency of Deism
Deism is inconsistent in a number of ways: (1) Miracles. Deism denies the existence of miracles while affirming the act of creation (which itself is a miracle). As one philosopher writes, “Why claim that the God who created the world from nothing does not have the ability to make something out of something (such as wine from water)?” . Internal inconsistencies flow even more so when consideration of natural law and God’s relation to the world are examined.
For example, deism has the central belief that either God (1) cannot intervene in the universe or (2) will not intervene in the universe. The differentiation between (1) and (2) is particularly that of a “hard” and “soft” definition of deism. If (1) is the case, then God as argued from others, is either stupid or cruel. In Richard Deems’ paper, Why Deism Fails as a Philosophical Paradigm for the Universe (2008), he argues the following:
According to deism, God is restricted by the laws of the universe. So, one has to ask how those laws got there? If God created the universe (a central tenet of deism), then He created the laws by which the universe operates. If God created the laws, why couldn’t He suspend them? Why would God create a universe in which He was personally unable to participate? Maybe the god of deism was too stupid to create a universe in which he could personally interact. Alternatively, maybe the god of deism created a universe just to watch the “fish” in the “fishbowl,” which seems a lot more cruel than the God of theism, who has a purpose for evil. So, the god of deism is either stupid or cruel or both. Such a god seems unnecessary in the overall scheme of the universe. 
Though I would admit that this is a more crude version of the argument that could be easily otherwise stated, the matter is clear. If God did create natural laws, then why is it the case that He can not intervene within them? It may be argued that this is a matter of either (a) Impotence or (b) Stupidity – though I surely might tend to argue the former.
-  Thomas Jefferson, The Jefferson Bible (N. D. Thomas Publishing Co., 1902) preface.
-  Diarmaid McCulloch, Christianity: The First Three Thousand Years (Penguin Group: 2009)
-  Ibid. p. 786
-  Ibid. p. 786
-  First published in The Spectator, no. 465 (1712). The original text, Psalm 19:1-6.
-  Francis Schaeffer, How Should We Then Live? (L’Abri 50th Anniversary Edition, 2005)
-  Ibid. p. 121
-  Ibid. see p. 120 and 122
-  Norman Geisler, Introduction to Philosophy: A Christian Perspective (Grand Rapids: MI, 1980) p. 276
-  From Gita May in the Introduction to Voltaire’s Candide (Barnes & Noble Classics, trans. Henry Morely: 2003) xvi
-  Norman Geisler, Introduction to Philosophy: A Christian Perspective (Grand Rapids: MI, 1980) pp. 276-27
-  From http://www.godandscience.org/apologetics/deism.html, last updated Sept. 2008