[continued from here]
... Therefore this Synod of Dordt in the name of the Lord pleads with all who devoutly call on the name of our Savior Jesus Christ to form their judgment about the faith of the Reformed churches, not on the basis of false accusations gathered from here or there, or even on the basis of the personal statements of a number of ancient and modern authorities — statements which are also often either quoted out of context or misquoted and twisted to convey a different meaning — but on the basis of the churches' own official confessions and of the present explanation of the orthodox teaching which has been endorsed by the unanimous consent of the members of the whole Synod, one and all.
Moreover, the Synod earnestly warns the false accusers themselves to consider how heavy a judgment of God awaits those who give false testimony against so many churches and their confessions, trouble the consciences of the weak, and seek to prejudice the minds of many against the fellowship of true believers. ...
(Conclusion, in the Canons of the Synod of Dordt)
Classical Arminianism refers to the belief system of the Remonstrants, especially as codified in the Remonstrant Articles and Opinions. Her founder, James Arminius, did not always share the same view as what Classical Arminianism in the Remonstrants taught — as seen most notably in Arminius' uncertainty regarding the doctrine of Eternal Security , while the Remonstrants rejected it outright . This must be seen as the slow [d]evolution of Classical Arminian theology, from Arminius who started off rejecting parts of Reformational theology, followed by the Classical Arminianism of the Remonstrants, and then on to later Remonstrants like Limborch with a steady drift leftwards.
Among the declension of ArminianismS, there would most definitely be a variety of views of what exactly each Arminian believes. For Classical Arminianism however, such a system must be defined especially by the Arminianism formed around the time of the Synod of Dordt, and expressed most notably in the Remonstrant Articles and Opinions, the confessional statements that were "squeezed" out of the Remonstrants (who through being ambivalent were not forthcoming with their views and tried as much as possible to forestall a synod being convened to examine their views, even though they were creating havoc in the Dutch Reformed churches  ).
In the Remonstrant Opinions, a Remonstrant creedal statement was obtained from the Remonstrants "only with difficulty" . In this creedal statement, the doctrines of Classical Arminianism were properly delineated, and their distinctive parts shown as follows :
(1) Partial depravity
(Therefore God has not with this plan created in the one Adam all men in a state of rectitude, has not ordained the fall and the permission of it, has not withdrawn from Adam the grace which was necessary and sufficient, ... –The Remonstrant Opinions A3. Bold added.)
(2) Conditional election
(The election of particular persons is decisive, out of consideration of faith in Jesus Christ and of perseverance; not, however, apart from a consideration of faith and perseverance in the true faith, as a condition prerequisite for electing. –The Remonstrant Opinions A7. Bold added.)
(3) Universal Atonement
(The price of redemption which Christ offered to God the Father is not only in itself and by itself sufficient for the redemption of the whole human race but has also been paid for all men and for every man, according to the decree, will, and the grace of God the Father; therefore no one is absolutely excluded from participation in the fruits of Christ’s death by an absolute and antecedent decree of God. –The Remonstrant Opinions B1. Bold added.)
(4) Resistible Grace
(The efficacious grace by which anyone is converted is not irresistible; and though God so influences the will by the word and the internal operation of His Spirit that he both confers the strength to believe or supernatural powers, and actually causes man to believe – yet man is able of himself to despise that grace and not to believe, and therefore to perish through his own fault. –The Remonstrant Opinions C5. Bold added.)
(5) Conditional perseverance in the faith
(True believers are able to fall through their own fault into shameful and atrocious deeds, to persevere and to die in them; and therefore finally to fall and to perish. –The Remonstrant Opinions D4. Bold added.)
The errors of Classical Arminianism are many. Besides the errors stated above, its humanistic slant is seen especially in the work of Grotius for example . Classical Arminianism also has a problem with the doctrine of Justification by Faith Alone in the doctrine of imputation (by making faith credited as righteousness instead of Christ's righteousness imputed as our righteousness) .
The concepts of Justification and Imputation is linked to the doctrine of sin and depravity, and ultimately to the Gospel. This is one of the the reasons why Classical Arminianism is serious heresy, because they explicitly undermine a key tenet of the Gospel: that of the sinfulness of Man.
The Remonstrant Opinions revealed that Classical Arminianism taught the error of Partial Depravity. In his polemic against Arminianism as it reared its ugly head in England, the Puritan scholar John Owen produced a booklet entitled A Display of Arminianism  to combat this heresy. Quoting from the Classical Arminians of his day and refuting their arguments, Owen has incidentally given us a window into what these Classical Arminians taught.
In his book, Owen devoted a chapter Of Original Sin  to examining the doctrine of sin and imputation held to by the Classical Arminians, where Classical Arminianism's doctrine of the non-imputation of sin is shown.
Quoting the Arminian Venator, it was said that "Infants are simply in that estate in which Adam was before his fall, ..." (p. 70). Boraeus states that "Adam sinned in his own proper person, and there is no reason why God should impute that sin of his unto infants" (p. 72). Corvinus affirmed that "That it is absurd, that by one man's disobedience many should be made actually disobedient" (p. 73). In the Remonstrant Apology, they have even said that "We confess that the sin of Adam may be thus far said to be imputed to his posterity, inasmuch as God would have them all born obnoxious to that punishment which Adam incurred by his sin, or permitted that evil which was inflicted on him to descend on them" , and "We account not original sin for a sin properly so called, that should make the posteriority of Adam to deserve of Adam to deserve the wrath of God, nor for an evil that may properly be called a punishment, but only for an infirmity of nature" .
All of these evidences Owen collected and deduced their view of original sin. Original sin as historically defined is the imputation of Adam's sin unto the whole human race without respect to the actual sinning of anyone - this the Classical Arminians deny. Rather, especially as seen in the case of infants, infants are born without the stain of original sin (guilt). Through the use of the concept of "prevenient grace", all infants are stated to be born without the guilt of sin. As Owen states, the Classical Arminians redefine Original Sin to mean "a defect of nature, and not of this or that particular person" (p. 73).
Therefore, in Classical Arminianism, all men are born with an "original sin nature" (thus an "infirmity of nature"), but without "original guilt". Sin is genetic rather than federal, transmitted but not imputed. Infants therefore are said to be actually sinless but possessing a sinful nature, and it is from this errant notion that the entire Arminian notion of "an age of accountability" is derived, not to mention the teaching that infants by default go to heaven.
On the topic of sin, justification and imputation then lies a most pernicous error in Classical Arminianism, which makes it heresy. It is not simply a denial of Predestination that makes Classical Arminianism heresy, but its denial of Original Guilt, the doctrine of the imputation of Adam's sin etc which stands behind their teaching of Partial Depravity, which makes it heresy indeed.
In the next section, we would do some comparisons with Evangelical Arminianism to see the differences between these two which are often confused with each other, and see why Evangelical Arminianism is EVANGELICAL and thus orthodox, while Classical Arminianism is not.
 James Arminius (1560 - 1609), The Works of James Arminius, vol. 1, 2.5.6 A Declaration of the Sentiments of Arminius on: The Assurance of Salvation. Accessed on CCEL.
 Appendix H — The Remonstrant Opinions D4, as cited in Peter Y. De Jong (ed.), Crisis in the Reformed Churches: Essays in Commemoration of the Great Synod of Dordt 1618-1619 (Grandville, MI, USA: Reformed Fellowship, 1968, 2008), p. 267
 Peter Y. De Jong (ed.), Crisis in the Reformed Churches, pp. 50- 51, 148-149
 Introduction in Appendix H — The Opinions of the Remonstrants, in Peter Y. De Jong (ed.), p. 261
 Appendix H — The Opinions of the Remonstrants, in Peter Y. De Jong (ed.), pp. 261-268.
 Marten H. Woudstra, The Synod and Bible Translation, in Peter Y. De Jong (ed.), pp. 132-134.
 Louis Praamsa, The Background of the Arminian Controversy (1586 - 1618), in Peter Y. De Jong (ed.), p. 48, states:
Arminias interpreted the doctrine [of justification] as teaching that man is justified before God not on the basis of the imputed righteousness of Christ but by the human act of believing which constituted his righteousness before God.
In his book, Arminian Theology: Myths and Realities (Downers Grove, IL, USA: IVP Academic, 2006), pp. 200-220, Roger E. Olsen tried to spin Arminius' teaching by saying that Arminius cannot mean this because he contradicted himself by stating an orthodox formulation elsewhere. This of course begs the question why one must read it in a Olsen's manner instead of the other way round, especially since some of the later Arminians interpret Arminius' phrase "faith imputed for righteousness" as precisely the error that human faith is considered as righteousness in God's sight, as Olsen himself admits (ie. Philip Limborch, Richard Watson, William Burton Pope, H. Orton Wiley). Despite Olsen's spin, the historical facts are unequivocal that Classical Arminianism is in error at this point.
 John Owen, A Display of Arminianism — A Discovery of the Old Pelagian Idol Free-Will, with the New Goddess Contingency, Advancing Themselves into the Throne of the God of Heaven, to the Prejudice of His Grace, Providence, and Supreme Dominion over the Children of Men (Originally published in 1644; Dahlonega, Georgia, USA: Crown Rights Book Company, Reprinted 1999)
 Owen, Chapter VII Of Original Sin and the Corruption of nature, pp. 68 - 82
 As quoted in Owen, p. 74
"Fatemur peccatum Adami, a Deo posse dici imputatum posteris ejus, quatenus Deus posteros Adami eidem malo, cui Adamus per peccatum obnoxium se reddidit, obnoxios nasci voluit; sive quatenus Deus, malum, quod Adamo inflictum erat in poenam, in posteros ejus dimanare et transire permisit." — Rem. Apol. p. 84
 As quoted in Owen, p. 75
"Peccatum itaque originale nec habent pro peccato proprie dicto, quod posteros Adami odio Dei dignos faciat, nec prop malo, quod per modum proprie dictae poenae ab Adamo in posteros dimanet sed pro infirmitate," etc. — Rem. Apol. fol. 84