*98Epworth Children’s Home appeals from an order construing the will of R. P. Byrd, Sr., in favor of the testator’s son, R. P. Byrd, Jr. The questions involved are whether Epworth or R. P., Jr., is entitled to the remainder interest in a trust established by R. P., Sr., for his other son, George S. Byrd and whether R. P., Jr., is collaterally estopped from litigating this issue. The trial judge held the remainder interest passed as intestate property to the only surviving heir of R. P., Sr., his son, R. P., Jr. We affirm.
R. P. Byrd, Sr., died testate in 1928 leaving a wife and two sons, George and R. P., Jr. His will established a trust for each son to be held during the son’s life. George died in 1981 survived by his wife Marvel and his brother R. P., Jr. George never fathered a child. Both Epworth and R. P., Jr., claim the remainder interest in the trust established for George.
I.
Epworth bases its claim to the trust assets on the following paragraph in Item 3 of the will:
Should the said beneficiaries or either of them die leaving an [sic] wife and a child or children then the title to the property hereinbefore provided for them shall vest in fee simple in his or their heirs, provided, however, that should the wife of either, or both of said beneficiaries die leaving no issue, child or children on [sic] my said son or sons, then the wife or wives of either of the said beneficiaries to be vested with only a life estate in the property hereinabove provided for my said sons, respectively, with remainder over, after their death to the Official Board of Epworth Orphanage, an institution of the Methodist Church located at Columbia, S. C., to have and to hold the same in fee simple for the benefit of the said institution.
The will mentions Epworth nowhere else.
An earlier provision in the same item provides:
It is distinctly understood, that the trust herein provided shall be a permanent one, that it is to say: to hold under said trust the said [sic] premises for and during the term of the natural life of the said beneficiaries, George S. Byrd and R. P. Byrd, Jr., and should either of *99my sons predecease the other, then, and in such event, the title to the property provided for my said son, George S. Byrd, under the trust (should he without wife or issue, predecease my son, R. P. Byrd, Jr.) shall vest in my said son, R. P. Byrd, Jr.; and should my said son R. P. Byrd, Jr., without wife or issue, predecease my son, George S. Byrd, then, the provision of the trust provided for R. P. Byrd, Jr., shall vest in the said George S. Byrd.
A court’s primary purpose in construing a will is to discover and give effect to the testator’s intent. May v. Riley, 279 S. C. 248, 305 S. E. (2d) 77 (1983). Where the language of the will is clear and unambiguous, the testator’s intention must be ascertained from the language used. Shelley v. Shelley, 244 S. C. 598, 137 S. E. (2d) 851 (1964). Although there is a presumption against intestacy, the presumption will not be applied where the plain and unambiguous language of the will effects an intestacy. 95 C. J. S. Wills, § 615b at 839 (1957); see Albergotti v. Summers, 203 S. C. 137, 26 S. E. (2d) 395 (1943). A court may not “by judicial construction make a will for the decedent that he has not made for himself.” Coffman v. Coffman, 85 Va. 459, 466, 8 S. E. 672, 675 (1888); 80 Am. Jur. (2d) Wills § 1128 at 238 (1975); see MacDonald v. Fagan, 118 S. C. 510, 111 S. E. 793 (1922). In interpreting a will, a court can derive little or no help from prior decisions in other will cases. “The epigram of Sir William Jones, ‘no will has a brother,’ remains true today.” Moore v. Hunter, 46 N. C. App. 449, 455, 265 S. E. (2d) 884, 887 (1980).
As we view the language in the item at issue, the testator plainly provided that a son’s wife was to have a life estate and at her death Epworth was to have a remainder in the property left in trust for the son only if the property passed to the son’s wife and child or children and the wife outlived the child or children. To afford the provision any other interpretation would be to rewrite the will.
Our construction of the will is consistent with what we perceive to be the primary intention of the testator. He clearly intended to give preference over third parties to his children first and to his other descendants second. For instance, the other quoted provision in the will shows that if either son were to die “without wife or issue” the trust would cross over to the other son.
*100Epworth suggests, and the dissenting opinion seems to imply, that the “provided, however” clause in the contested paragraph is an independent provision that disposes of the property intended by the testator for a son if the son dies leaving a wife but no child. We do not agree.
The “provided, however” clause is simply a part of the same sentence as the clause in which the testator devises certain property in fee simple to a son’s “heirs” if the son is survived by a “wife and a child or children.” It makes no new grant of an estate to a son’s surviving wife. Rather, the “provided, however” clause simply clarifies the testator’s intention to give a daughter-in-law as an heir of his son “only a life estate in the property” if a son dies “leaving [a] wife and a child or children” and the wife outlives the son’s child or children. Cf. Johnson v. Waldrop, 256 S. C. 372, 182 S. E. (2d) 730 (1971) (subsequent words in a will can cut down a fee when the testator’s intent is clear and unmistakable).
Moreover, the “provided, however” clause cannot stand on its own. The clause does not mention any event, such as the death of a son, that would trigger a disposition of trust property to a son’s wife. It simply addresses a situation that might exist at the death of a son’s wife and not at the death of a son and it serves, as we have noted, to limit a gift to a son’s wife.
Epworth’s secondary contention is that the word “and” means “or” where the will refers to a son leaving a “wife and a child or children.” Under this interpretation, trust property could pass to a son’s wife as a son’s “heir” and the wife would be vested with a life estate while Epworth would hold the remainder.
We recognize that on occasion our Supreme Court and others have read the conjunction “and” to mean “or” and vice versa when construing a will. See, e.g., Albergotti v. Summers, 205 S. C. 179, 31 S. E. (2d) 129 (1944); Wood v. Wood, 132 S. C. 120, 128 S. E. 837 (1925); Massey v. Davenport, 23 S. C. 453 (1885); Duncan v. Harper, 4 S. C. 76 (1873); 80 Am. Jur. (2d) Wills § 1161 at 277 (1975). The word “and” will be used disjunctively, however, only where the entire will clearly indicates the testator intended a contrary meaning. Albergotti v. Summers, 205 S. C. 179, 31 S. E. (2d) 129 *101(1944); 95 C. J. S. Wills § 613b at 820 (1957). “This latitude of construction is not to be exercised where the language of the will is explicit and the intent of the testator is not doubtful, but will be resorted to only when necessary in order to support the evident meaning of the testator.” 80 Am. Jur. (2d) Wills § 1161 at 278 (1975).
Considering the will here involved as a whole and particularly the preference shown by the testator toward his descendants, we cannot say the testator clearly intended to use the word “and” in any way but its usual conjunctive sense.
Furthermore, changing the word “and” to read “or” is not necessary to support the testator’s evident meaning. Indeed, for us to construe the word “and” to mean “or” would expand the provision’s application. The provision would apply not only to the case of a son leaving a wife and child but also to the cases of a son leaving a wife only and a son leaving a child only.
We decline, then, to interpret the word “and” to mean “or.”
Because the will does not address the situation that actually occurred, George dying survived by only a wife, we hold that a partial intestacy exists in the Estate of R. P. Byrd, Sr., and that the trust assets pass by intestacy to the testator’s only surviving heir, his son R. P., Jr.
II.
As we gather, Epworth also argues that a decree entered on October 24, 1944, by the late Honorable L. D. Lide in an action entitled Parker et al., Trustees v. George S. Byrd, R. P. Byrd, Jr., et al., precludes litigation by R. P., Jr., in this action of the issues actually and necessarily litigated and determined in the Parker action. One issue Epworth claims was litigated and determined in the Parker action was the proper interpretation to be given the will provision questioned here. Judge Lide’s decree makes the following observation about the provision:
The language of the will is not entirely clear, but I think it may be correctly construed as providing further that if either of the beneficiaries should die leaving a wife and a child or children then the title to the property provided for him (including what he may have *102received, if anything, as survivor of his brother) would vest in fee simple in his heirs, but if he should leave a wife only, the wife would be vested with a life estate only, with remainder over in fee simple to the “Official Board of Epworth Orphanage.”
We need not decide, however, whether the Parker action precludes R. P., Jr., from litigating in this action the issue concerning how the will provision in question should be construed. Ordinarily, the defense of estoppel by prior adjudication is an affirmative defense that must be pled. Shecut v. Shecut, 257 S. C. 354, 185 S. E. (2d) 895 (1971); Wagner v. Wagner, 335 S. E. (2d) 246 (S. C. Ct. App. 1985); Lindler v. Baker, 280 S. C. 130, 311 S. E. (2d) 99 (Ct. App. 1984). Here, Epworth did not plead the defense.
In any event, Epworth failed to show that Judge Lide’s interpretation of the will provision at issue in this case was necessary to support the judgment in the Parker action; therefore, R. P., Jr., was not collaterally estopped from litigating the question of its interpretation in the instant action. Beall v. Doe, 281 S. C. 363, 315 S. E. (2d) 186 (Ct. App. 1984).
Affirmed.
Sanders, C. J., concurs with separate opinion. Gardner, J., dissents with separate opinion.